Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 1 of 37 0845 600 8951
BNWAT05: Rainwater & greywater
systems - Supplementary briefing
note
Version 1.0
This Briefing Note and referenced information is a public consultation document and
will be used to inform Government decisions. The information and analysis forms
part of the Evidence Base created by Defra‟s Market Transformation Programme.
1 Introduction
Rainwater harvesting (RWH) and greywater reuse systems provide non-potable supplies of
water to buildings. By providing an alternative source of water they can help new and
existing buildings reduce demand for mains water supply. These standards may be imposed
by regulatory or local planning requirements. However, the feasibility of these systems in
new and existing buildings must be considered fully prior to development.
The information in this note is for England and Wales as Defra and Welsh Assembly
Government policies and actions may not be applicable in Scotland and Northern Ireland.
The information may be used to inform feasibility studies.
1.1 Purpose of the briefing note
This briefing note defines rainwater harvesting and greywater reuse system technologies
and presents the barriers and opportunities to increased uptake. This note is consistent with
other water sector Market Transformation Programme (MTP) briefing notes by focusing on
domestic households, but also considers the non-household sector. The overall purpose of
this briefing note is to increase uptake of rainwater and greywater systems in situations
where these are technically and financially feasible. It aims to do this by providing the key
facts on both of these technologies: definitions; product types and performance; best
practice installations and yield methodologies; availability and pricing; applicability in
different building types; and future changes in product and policy development.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 2 of 37 0845 600 8951
1.2 MTP Goals
Sustainable water management is essential to protect the water environment and to meet
current and future demands for water. The key to water efficiency is reducing waste, not
restricting use.
At present, most buildings are supplied with potable water (i.e. wholesome water fit for
drinking) from the public water supply network. Much of this is used in activities where non-
potable water would suffice. For example, in many existing homes, toilet flushing is
estimated to account for around 30 per cent of the household‟s daily demand (although data
from water companies indicates that this average is falling to 26 per cent1 as more new
homes are built to higher standards of water efficiency and older WCs in existing homes are
replaced with lower flush models). In non households toilet flushing may be a much higher
proportion of domestic-type demand.
1.3 Content of the briefing note
This briefing note contains the following information:
Section Information
1: Introduction 1.1 Purpose
1.2 Goals
2: Drivers 2.1 Water availability
2.2 Housing growth
2.3 Building Regulations and the Code for Sustainable Homes
2.4 Surface water management
3: Definitions Definitions and terminology
4: Water use in the home 4.1 How much can be saved
5: Product standards 5.1 BSI Rainwater code of practice
5.2 BSI Greywater code of practice
5.3 Related water regulations
6: Determining feasibility 6.1 Building characteristics
6.2 Economic Factors
6.3 Social Factors
6.4 Opportunities and barriers
7: Sustainability Energy and carbon
8: Innovation Integrated systems
9: Recommendations and action plans
Actions to increase uptake, actions to improve MTP data
Appendix A Product descriptions
Appendix B Environmental benefits
1 BNWAT01 WCs:Market projections and product details
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 3 of 37 0845 600 8951
2 Drivers
2.1 Water Availability
Annual average rainfall in England and Wales varies between less than 700 mm to over
2000 mm per year2. Whilst this is plentiful in some areas (e.g. the north and west of the
country), these rainfall totals have to be put in the context of the demand for water from a
population of approximately 54.8 million3.
The total volume of water that is abstracted every day by the water companies in England
and Wales is 14,449 Ml/d4. Two thirds of this (approximately 75 per cent) is supplied to
households and non households, and the vast majority of this is for domestic use.
However, water is a finite resource and three factors are increasing the pressure upon
existing water resources:
The population is expected to continue growing, particularly in the south-east of
England and there is a trend towards single occupant dwellings. This has been shown
to increase pcc5;
The impact of climate change which UK Climate Projections predicts will reduce
summer rainfall6 and which may at the same time increase climate influenced
demands, such as personal washing; and
Increasing availability of more consumptive water using products such as power
showers, and consumptive behaviours, e.g. increased personal washing. Water
companies‟ Water Resource Management Plans contain strategies specifically aimed
at trying to reduce per capita consumption (pcc). Several water companies have
reported pcc levels that are far above 150 litres per day.
2.2 Housing growth
Significant housing growth is planned for the next 10 to 15 years. The number of households
in England is projected to grow to 27.8 million in 20317, and to a total of 29.2 million in
England and Wales, an increase of 6.3 million (29 per cent) over the 2006 estimate, or
252,000 households per year. This has the potential to increase the demand for potable
water. In particular, development in the south and east will add significant pressure on water
supply in the most water-stressed region of the country.
2 http://www.metoffice.gov.uk/corporate/library/factsheets/factsheet09.pdf
3 http://www.statistics.gov.uk/statbase/Product.asp?vlnk=15106
4 Water UK Water Supply and Infrastructure Data http://www.water.org.uk/home/resources-and-
links/waterfacts/waterindustry/data 5 Herrington (1996). Climate change and the demand for water.
6 UK Climate Projections 2009. Online climate change projections report.
http://ukclimateprojections.defra.gov.uk/content/view/2068/500/ 7 http://www.communities.gov.uk/documents/statistics/pdf/1172133.pdf
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 4 of 37 0845 600 8951
More detail on population and housing growth forecasts is available in BNWAT06: Domestic
water use in new and existing buildings.
2.3 Building Regulations (Part G) and the Code for Sustainable
Homes
The Code for Sustainable Homes and the 2009 amendment to the Building Regulations set
whole building consumption standards for new homes. Part G of Schedule 1 of the Building
Regulations (2000) stipulates that in new dwellings:
“reasonable provision must be made by the installation of fittings and fixed appliances
that use water efficiently for the prevention of undue consumption of water”.
Regulation 17K specifies:
“the potential consumption of wholesome water by persons occupying [the new]
dwelling must not exceed 125 litres per person per day..,[calculated according to the]
Water Efficiency Calculator for New Dwellings”.
The revised Building Regulations are in-line with Level 1/2 of the Code for Sustainable
Homes, with an allowance of five litres per head per day for external use:
Level 1/2 for water is defined as 120 litres/person/day;
Level 3/4 for water is defined as 105 litres/person/day; and
Level 5/6 for water is defined as 80 litres/person/day.
It is generally accepted that achieving level 3/4 of the Code for water can be achieved by
installing an appropriate combination of water efficient fixtures and fittings, and continuing to
influence consumer behaviour. It does not require installation of rainwater or greywater
systems and the cost to deliver a new home to CSH level 3/4 could be approximately £125
per house above the cost of construction of a house to meet the CSH Level 1/2 performance
standard of 120 l/h/d (CLG, 20088). What is important is that achieving CSH level 5/6
standard of 80 litres per head per day (or lower) is likely to require some form of non-potable
water input to domestic properties, e.g. harvested rainwater or reused greywater.
Future developments, particularly in the most water stressed parts of England and Wales,
may require new households to be designed and built to achieve consumption rates at level
5/6 of the Code for Sustainable Homes (80 litres per head per day). This level of water
efficiency is very likely to require some form of rainwater harvesting or greywater reuse. The
nature and design of such systems will depend on wide number of factors, and the success
of these systems will require co-operation from a large number of stakeholders, including
planners, developers, water companies, and others.
8 CLG (2008). Cost Analysis of The Code for Sustainable Homes. Final Report
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 5 of 37 0845 600 8951
2.4 Surface water management
In addition to water resources issues, there are also concerns about rainwater drainage from
urban areas. Planning authorities are required to consider the effects of development on
surface water drainage and the potential impact on flood risk, (Planning Policy Statement
259). The suitability and sustainability of developments will increasingly be judged, in part,
on their requirements for water supply and wastewater removal. Rainwater harvesting has
the potential to provide benefits in the form of attenuating rainfall and minimising surface
water run-off. Further, BRE, which manages the Code on behalf of Communities and Local
Government, has issued guidance that includes consideration of the use of rainwater
harvesting systems to contribute to surface water management, “where infiltration cannot
reduce all of the additional volume [surface water] ….. must evaluate the appropriateness of
rainwater harvesting systems to reduce the residual additional volume by diverting water for
use within the dwelling”10.
Further information on environmental benefits of rainwater harvesting and greywater reuse is
provided in Appendix B.
9 http://www.communities.gov.uk/publications/planningandbuilding/pps25floodrisk
10 BRE (2009). Code for Sustainable Homes – Technical Guidance Note 001 Supplementary
guidance on the assessment of the Management of Surface Water Runoff criteria (SUR 1). http://www.breeam.org/filelibrary/Sur__1__Guidance_note__v12__2_.pdf
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 6 of 37 0845 600 8951
3 Definitions
Wholesome water means water complying with the requirements of regulations made under
Section 67 (standards of wholesomeness) of the Water Industry Act 1991.
Non wholesome water means water that does not meet the requirements for wholesome
water, but is considered suitable for certain applications having regard to the risks to human
health. This could include greywater or harvested rainwater11.
Rainwater is that arising from atmospheric precipitation12.
Rainwater harvesting
The principle of rainwater harvesting is that rainwater is collected from roof areas and/or
areas of hard-standing, treated as appropriate, then pumped, direct or via a header tank, to
or within individual buildings. This water can be used without disinfection for non-potable
applications such as toilet flushing, outside water use, and non-hygiene cleaning. It can be
used for washing machines, although there may be occasional colour and odour issues,
depending on the quality of water collected. A mains supply must be provided for when
there is no rainwater in the storage tank.
Water butts are useful simple systems to provide water for gardens but these are not
included within the MTP definition of a rainwater harvesting system.
Greywater is domestic wastewater excluding wastewater arising from the WC. It is generally
collected from baths, showers and washbasins and may also be collected from kitchen
sinks, although the level of contamination from foodstuffs and other sources usually preclude
the use of kitchen wastewater. After basic treatment, greywater may be used for purposes
around the home such as toilet flushing or garden watering that do not require water of
potable water quality.
Greywater reuse is the use of untreated greywater for purposes that do not require potable
water.
Reclaimed water
Unlike greywater, reclaimed water is that which has not been supplied via the mains, e.g.
untreated borehole water. It is collected and treated for specific non-potable uses such as
flushing WCs.
SuDS
Sustainable drainage measures which alleviate flood risks both at a development site and
elsewhere in the catchment.
11
Building Regulations Part G General Guidance 12
BS 8515: 2009. Rainwater harvesting systems – Code of practice.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 7 of 37 0845 600 8951
4 Water use in the home
When considering the implementation of alternative supply systems within new buildings it is
important to understand domestic water use patterns. Data on household water use is
available in the water company Water Resource Management Plans. Figure 4.1 represents
the average data from those water companies that have undertaken customer use surveys
and other forms of data collation.
It shows that toilet flushing is the largest single use of water (26 per cent of total demand),
with personal washing (showers, baths and taps) accounting for a further 42 per cent.
Washing machines also account for a significant percentage of the total volume at 10 per
cent. The remaining third is consumed via washing up in kitchen sinks (7 per cent), outdoor
use (9 per cent), and other miscellaneous uses (6 per cent).
As defined in Section 1.2, rainwater is suitable for uses that do not require potable water
quality such as WC flushing and outside use (in total approximately 35 per cent of household
use). Greywater is suitable for WC flushing.
Figure 4.1 Water use in the home
Bath use, 14%
Shower use,
19%
Toilet flushing,
26%
Clothes
washing, 10%
Garden use, 8%
Car washing,
1%
wash basin, 9%
Miscellaneous
use, 6%
Dish washing,
7%
Source: Micro-component data from the water companies 2009 Water Resource Management Plans.
4.1 How much water can be saved
The environmental drivers for saving water and reducing demand for mains supplies are
clear. The question is;
How much water can be saved through rainwater harvesting and greywater reuse?
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 8 of 37 0845 600 8951
On average, each person in England and Wales uses just over 150 litres of mains drinking
quality water every day, so a family of four uses around 220,000 litres per year. In theory, of
this average mains water use, approximately 44 per cent is used for WC flushing, supplying
the washing machine and watering the garden13. This mains water usage could be
substituted with harvested rainwater or treated greywater. There are some concerns over the
use of harvested rainwater for clothes washing mainly that the quality of the water could
damage clothes but these are not prohibitive and may be resolved.
7,599 Ml of potable water is supplied to households in England and Wales each day and up
to one third of this is used to flush toilets. Savings are highly dependent on supply being
sufficient to meet demand and uptake, rainfall patterns, collection systems, and personal
habits (particularly for greywater reuse) will limit the maximum potential from being realised.
However, if just one per cent of all homes used an alternative source of water to flush the
toilet 22.8 Ml/d of water would be saved.
Rainwater can be used to flush toilets and wash clothes if there is sufficient yield and
storage capacity. This is dependent on rainfall and how much of this can be collected and
so savings may vary throughout a year. The installation of a greywater reuse system should
provide more than adequate supply for toilet flushing, and potentially save 20 per cent of
internal household use, in a house already fitted with a highly water efficient WC (e.g. 4.5
litre single flush, or 4/2.6 litre dual flush toilet)14.
4.1.1 Calculating water demand and yield of non-potable technologies
Rainwater harvesting is a simple concept. Rainwater is channelled directly from the
surface(s) it falls on. Once collected and stored it can be used for non-potable purposes.
From a holding tank from the water is fed to the point of use, either by gravity (if the tank is
stored at a level above the point of use), or by a small pump. The volume required is a
function of the demand for non-potable water.
CIRIA15 and the Environment Agency16 have published guidance on how demand and yield
for rainwater harvesting systems should be calculated. The recommended formula is
presented below:
13
Analysis of water company 2009 Water Resource Management Plan micro-component data (survey
based) 14
London Development Agency (2009). Managing Water - Reducing Water Demand. Technical Report (Entec, unpublished).
15 CIRIA (2001) Rainwater and Greywater Use in Buildings: Best Practice Guidance. Report C539. CIRIA, London
16 Environment Agency (2010). Harvesting rainwater for domestic uses: an information guide. Environment Agency. Bristol
Annual rainfall (mm) x effective collection area (m2) x drainage coefficient (%) filter
efficiency (%) x 0.05
(Environment Agency (2010). Harvesting rainwater for domestic uses: an information guide).
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 9 of 37 0845 600 8951
This calculation takes account of:
Annual rainfall totals and the temporal variation in rainfall in the specific site location;
The effective collection area (m2) (equal to the area of roof and/or hard-standing that
can be reasonably used to collect rainfall);
A drainage coefficient (based on type of roof and other catchment materials, and the
proportion of actual rainfall that can be collected, allowing for surface wetting,
evaporation and excess runoff during intense storm events); and
Filter efficiency; of the water that is collected in the gutters not all will reach the
holding tank. (manufacturers usually advise that 90% of the water flowing into the
filter is retained).
The feasibility of greywater systems is independent of rainfall and less likely to be affected
by occupancy rate. However, it could be that occupants of a single in-house system use
only a small amount of water for bathing and spend the majority of the day at home,
therefore using a larger amount of water for flushing the toilet. This would create a higher
demand for treated greywater than the quantity available and would also lead to minimal
water savings.
Unlike rainwater systems which are heavily dependent on the dimensions of a building to
generate sufficient yield, and in general the feasibility of greywater is affected more by the
performance and perception of the technology. The following formula calculates the demand
and the yield of greywater systems:
Feasibility assessments also need to consider the energy impacts of moving water around a
property for reuse.
4.1.2 Current Ownership
Around 2000 rainwater harvesting systems were installed in the UK in 2006/0717 and by
2010 this is believed to have increased (there are no data for England and Wales
specifically). Of these, 70 per cent were domestic systems18. The majority (> 95 per cent)
17
Environment Agency (2008). Harvesting rainwater for domestic uses: an information guide. Environment Agency. Bristol
18 Email communication, Rainwater Harvesting Association (October 2010).
Demand = per person daily average WC flush x occupants sharing greywater system
A second formula calculates the daily non potable supply (i.e. water from bath/shower)
Supply = per person personal washing demand* x occupants sharing greywater system
*Taken from the CSH Water Use Calculator
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 10 of 37 0845 600 8951
are sold for installation in new buildings. Retrofit rates are currently quite low since there are
few incentives to counteract the installation costs that are often prohibitive in existing
buildings. There may be some incentive from savings on water bills but these will only apply
to metered customers and may be limited due to the current low price per unit of water. One
of the main issues limiting retrofits is the physical constraint of accommodating a water
storage tank.
There has been a recent shift (2008-2010) in the types of developers who procure rainwater
harvesting systems from mainly self-builders and small developers to social housing
contractors and major developers in the UK19. This may demonstrate that rainwater
harvesting is moving from the small-scale peripheral market to more mainstream
developments. Social housing is a development sector that offers large scale potential for
improving water efficiency. The Code for Sustainable Homes was developed using the
Building Research Establishment‟s (BRE) EcoHomes System, which had already achieved
success in reducing the impact of affordable housing projects, in particular within the social
housing sector20. Waterwise has also made recommendations for the Government to
include water efficiency in the Decent Homes initiative, particularly by recommending water
efficient showers as a standard fitting21. The Code for Sustainable Homes now requires new
social housing developments to meet level 3/4 for water.
19
Email communication (October 2010): SCP Environmental Ltd 20
CLG (2006). Code for Sustainable Homes . A step-change in sustainable home building practice. http://www.planningportal.gov.uk/uploads/code_for_sust_homes.pdf 21
Waterwise (2009). Beyond Decent Homes. Memorandum. http://www.publications.parliament.uk
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 11 of 37 0845 600 8951
5 Product standards
An increase in the market for rainwater systems has led to Codes of Practice being
developed for rainwater and greywater systems. These standards are designed to ensure
that recycled water does not pose a risk to human health and have been produced in
response to the expansion in the rainwater harvesting and greywater reuse sector.
5.1 BSI Rainwater code of practice
BS 8515:2009 was published and came into effect on 31 January 2009. It sets out
recommendations on the design, installation, testing and maintenance of rainwater
harvesting systems supplying non-potable water in the UK. It covers systems supplying
water for domestic water uses (in residential, commercial, industrial or public premises) that
do not require potable water quality such as laundry, WC flushing and garden watering. It
does not cover systems supplying water for drinking, food preparation and cooking,
dishwashing and personal hygiene. A rainwater harvesting system with filtration conforming
to Section 4.3 of the standard will provide water of a suitable quality for WC flushing, laundry
and garden watering in most residential, commercial and industrial situations. However,
where greater human exposure to the water is anticipated or where the water is to be used
in public premises, this could require higher water quality. In such cases, the system may
incorporate treatment processes such as ultraviolet (UV) or chemical disinfection22.
5.2 BSI Greywater systems code of practice
The British Standard for greywater systems is divided into two parts. Part 1, BS 8525-
1:2010 Greywater Systems: Code of Practice came into effect on 30 June 2010. As a code
of practice, this first part of BS 8525 takes the form of guidance and recommendations. It
does not specify compliance requirements. Part 2, Part 2: Domestic greywater treatment
equipment – Requirements and test methods, will provide more detail on the specification of
treatment equipment and the procedures for testing system performance.
Part 1 of BS 8525 gives recommendations on the design, installation, alteration, testing and
maintenance of greywater systems utilising bathroom greywater to supply non-potable water
in the UK. It covers systems supplying water for domestic water uses (in residential,
commercial, industrial or public premises) that do not require potable water quality such as
laundry, WC and urinal flushing and garden watering. It also covers individual and
communal systems; and it applies to retrofitting and new build. It does not cover systems
supplying water for drinking, food preparation and cooking, dishwashing and personal
hygiene; direct reuse systems for external use; product design for specific system
components; or the reuse of trade effluent.
22
BS 8515:2009 Rainwater harvesting systems –Code of practice [Section 4.3]
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 12 of 37 0845 600 8951
5.3 Related water regulations
Water Supply (Water Fittings) Regulations 1999 in England and Wales.
If a rainwater harvesting system is inadequately installed, it could become a public
health hazard. Of specific concern is accidental contamination of mains water with
rainwater. The Water Supply (Water Fittings) Regulations 1999 aim to prevent this.
The main safeguard that the legislation requires is that a type AA air gap must be used
at the point where the mains top-up enters a rainwater harvesting system. A type AA
air gap ensures that there is a physical separation between the two types of water,
ensuring that no rainwater can be drawn back into the mains water supply23. The
Regulations also require appropriate marking of pipes that contain non-potable water.
WRAS Information and Guidance note 9-02-05 states that:
- It is important that all pipe-work supplying reused water is readily identifiable to
those who come across it for the first time;
- Pipe-work should be both recognisable and distinguishable from that supplying
mains water; and
- Pipes must be marked and labelled.
Building Regulations Part G. Part G24 covers sanitation and water efficiency, defines
wholesome and non wholesome water, it confirms that to be considered wholesome,
water must comply with the requirements of Section 67 of the Water Industry Act 1991,
and that the relevant regulations under this are:
- The Private Water Supplies Regulations 1991;
- The Water Supply (Water Quality) Regulations 2000 (SI 2000/3184) for
England; and
- The Water Supply (Water Quality) Regulations 2001 (SI 2001/3911) for Wales.
Building Regulations Part H. Part H covers drainage and waste disposal. The
regulations are that rainwater or greywater tanks should prevent leaks, have an anti-
backflow device, and be accessible for cleaning. The regulations also set out the
requirements regarding correct labelling of pipe-works and other measures to prevent
cross-contamination of water within the building.
Part H states that further guidance on systems for greywater and rainwater re-use can
be found in the Water Regulations Advisory Scheme (WRAS) leaflet number 09-02-04,
23
Environment Agency (2008). Harvesting rainwater for domestic uses: an information guide.
Environment Agency. Bristol 24
Building Regulations Part G General Guidance
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 13 of 37 0845 600 8951
Reclaimed Water Systems. Information about installing, modifying or maintaining
reclaimed water systems25.
As the market for rainwater and greywater systems is increasing, so too are the number of
manufacturers and the range of products that are available. Several sets of standards have
been developed in order to provide purchasers with guidance on the water efficiency of the
whole range of water using devices, and many of these include efficiency and/or
performance criteria for rainwater and greywater system products. These standards
distinguish between products in terms of water consumption/efficiency performance and
include:
The Water Technology List (WTL)26 (which underpins the Enhanced Capital Allowance
(ECA) scheme developed by the Department for Environment, Food and Rural Affairs
(Defra) and HM Revenue and Customs (HMRC). A qualifying rainwater harvester must
include: a storage level monitor; mains back up control unit; and a filter and storage
tank. A greywater system must enable recovery and on-site reuse of ≥ 40% of the
wastewater received by system;
The Bathroom Manufacturer‟s Association (BMA) Water Efficient Product Labelling
Scheme.27 The scheme provides access to a database of bathroom products which
when installed and used correctly will use less water, save energy and save money.
Currently only one greywater system is included in the BMA labelling scheme;
The Association of Environmentally Conscious Builders (AECB) develops & publishes
standards for sustainable building28. The AECB standards state that rainwater and
greywater systems are generally not recommended, but may be suitable for installation
under certain circumstances.
25
Published in 1999. January 2011 this is still a live document on the WRAS website:
www.wras.co.uk [publications] 26
www.eca-water.gov.uk 27
www.water-efficiencylabel.org.uk 28
www.aecb.net
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 14 of 37 0845 600 8951
6 Determining the feasibility of a non-potable supply
This section sets out the key factors that should be considered when determining whether a
non-potable supply system would be feasible in a property and the specific factors to
determine whether a rainwater or greywater option is most suitable.
The technical and economic feasibility of a system is based on:
The household/property demand for non-potable water;
The supply yield (i.e. rainfall for rainwater harvesting, or used potable water for
greywater reuse);
Demand and yield are heavily dependent on the type of building/development (building
dimensions, expected occupancy, types of water use);
Cost of technology (including installation), payback period, and maintenance costs.
The influence of cost factors on the decision to install a non-potable system is directly
related to the „ownership‟ factor, i.e. who will bear the costs, who will be required to
fund and manage maintenance, and who will benefit from the longer term payback;
The level of investment cost is affected by when non-potable options are considered in
the planning, design and development process, i.e. costs can be reduced or mitigated
when a system is integrated into a development at the planning and design stage.
There also other social factors that influence uptake of these technologies. Perceptions
regarding the reliability and quality of the non-potable water, health and safety concerns, and
attitudes towards householder maintenance of the water supply systems, all contribute to
user uptake and the effectiveness of non-potable water systems.
6.1 Building characteristics that affect demand and yield
The feasibility of rainwater harvesting and greywater reuse varies depending on the nature
of the development. Key factors include the overall nature of the building (e.g. high rise flats
compared to large detached houses), the density of residential units, the expected
occupancy rate, and the space available within a building and property (including garden) for
tanks, treatment, plumbing and control systems. A London Development Agency (LDA)
study29 considered six generic development types to examine the feasibility of these
technologies; three types of flat development, and three types of house developments. The
key defining characteristics are summarised below and the low water technologies that may
be applicable to each is presented in Table 6.1.
29
London Development Agency (2009). Managing Water - Reducing Water Demand. Technical
Report (Entec, unpublished).
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 15 of 37 0845 600 8951
The results (based on typical rainfall in London) suggested that rainwater harvesting is most
suitable to properties with a low ratio of expected occupants to roof catchment, i.e. low
density housing units with a large roof area.
Such developments are most commonly low rise apartment blocks or moderate to large
houses. In these situations, a communal system (up to five properties) may be more cost
effective in terms of tank size and yield.
Table 6.1 Summary of non-potable technology suitable for different household
building types.
Water
Efficiency
Measure
Luxury
High Rise
City Flats
Standard
Mid Rise
Flats
Low Rise
Flats
Small
Houses
Medium
Houses
Large
Houses
Rainwater
(toilet
flushing)
Possibly with
ratio of 1
resident: 25m2
roof
catchment.
Alternatively
use water
butts for
landscaping
Possible if occupant density
is 1:26m2 or less (most likely
if development includes large
surface area of mixed use
development to increase
yield).
Yes with 700-
800 litre storage.
However,
communal
system (5
houses) offers
better value for
money.
Yes. Reliability when using
for flushing and clothes
washing maybe less than for
toilet flushing only but the
overall savings make this a
feasible option for housing
types with occupant:
catchment ratios of 1:25m2+.
Storage tank between 800 to
1300 litres.
Rainwater
(toilet flushing
and washing
machine)
No No No
Greywater Yes. 100 litre storage is sufficient. Space is a
constraint. Careful planning at design stage is
essential.
Yes. 100 litre storage is sufficient. Less compact
(cheaper) systems may be acceptable as long as
included at design stage. Not in addition to
rainwater harvesting system (not cost effective).
In practice, most household roof areas are too small to satisfy all the potential demand for
rainwater, at all times of the year, regardless of practical storage tank capacity. It is therefore
important that the potential savings are fully evaluated before investing in an expensive
installation. In existing homes, it is generally more economic to reduce water use by fitting
more water efficient appliances and adopting water efficient behaviours before considering
the use of either rainwater (except a waterbutt) or greywater.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 16 of 37 0845 600 8951
6.2 Economic factors influencing uptake of non-potable
technologies
6.2.1 Capital expense
A key element that must be considered in the context of market transformation is product
pricing. If a product has a price premium associated with it then this is likely to negatively
impact on uptake. Rainwater harvesting companies have stated that the capital cost of
rainwater systems for retrofitting are generally considered very expensive and are not
appealing in terms of simple payback periods for a typical household. The companies go on
to report that if the house is being extended or extensively refurbished then it may be
possible to install a system and the cost is not much more than a system in a new build.
At present, water is relatively inexpensive in England and Wales, typically around 94 pence
per cubic metre (p/m3, with one cubic metre equal to 1,000 litres) for water delivered, and
119p/m3 for sewage collected30. The installation of an alternative domestic water supply is
quite costly, with an initial outlay of around £1,000 - £1,500 for a basic above ground
domestic system (2,600-3,600 litres storage)31. A wide range of costs are quoted by
rainwater harvesting companies, reflecting the different installations, with typical costs in the
region of £400 to £3450 per house at year 2000 prices32.
In addition to the cost of the equipment, there is also the cost of installation and maintenance
to consider. A rainwater harvesting system will require labour and excavation equipment to
install the storage tank and all the systems will require a trained plumber to install the
ancillary components and distribution pipe-work. An Environment Agency study reports that
the plumbing and fitting costs of installation can be around £1,00033.
However, rainwater harvesting companies have reported that the “costs for buying and
installing a system have decreased as the demand has increased. The largest reductions in
cost are available to sites in which multiple systems are required, such as social housing”34.
For larger commercial tanks of up to 100,000 litre capacity, tanks costs approximately
£10,000. Large scale housing developments with shared maintenance and infrastructure
are more likely to make systems financially attractive to install because of economies of
scale. Maintenance and operation costs listed as being typically in the order of £50-£160
30
http://www.ofwat.gov.uk/legacy/aptrix/ofwat/publish.nsf/Content/rpt_int_08unitcostswater.html [Table 6]
31 www.rainwaterharvesting.co.uk
32 Environment Agency (2008). Water related infrastructure for sustainable communities: Technological Options and Scenarios for Infrastructure Systems. Science project SC050025. Environment Agency. Bristol
33 Environment Agency (2010). Harvesting rainwater for domestic uses: an information guide. Environment Agency. Bristol
34 Email communications (October 2010). SCP Environmental Ltd
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 17 of 37 0845 600 8951
per year35. This can be reduced if householders are able to carry out some simple tasks
themselves such as:
Cleaning filters approximately three times a year, depending on tree cover over the
collection area;
Keeping gutters free of debris to prevent blocking the system; and
Visually inspecting the outside of the tanks for leaks etc at least once a year.
BS 8515 recommends checks once per year but these maintenance tasks may need to be
done more regularly as required.
However there are some elements of the maintenance that the householder will not be able
to carry out and where costs will be incurred. Entry into rainwater tanks should be avoided
unless absolutely necessary, and should only be attempted by a trained professional who
has the appropriate equipment and training to work in confined spaces.
The maintenance and repair of communal systems is a more ambiguous area. The topic
has been considered by the Construction Industry Research & Information Association
(CIRIA). The CIRIA report, Rainwater and Greywater Use in Buildings: Project Results From
The Buildings That Save Water Project; Best Practice Guidance36, provides advice on the
use and development of model operation and maintenance arrangements for both rainwater
and greywater systems. It also includes simple guidance on how to incorporate these
systems in developments.
Certain sectors of the market have seen prices for rainwater and greywater systems fall. The
single house system price has begun to fall in the past couple of years, driven by a few
factors: there are less well engineered systems being sold at a lower price to the larger
purchasers; there are many more suppliers in the market than there were, and this ultimately
drives prices down as the market becomes more competitive; and economies of scale also
assist in reducing prices37. The price of greywater reuse systems is likely to be negotiable
based on the number of units required and manufacturers keen to enter the new build
market.
Commercial developments can take advantage of the Government‟s Enhanced Capital
Allowance Scheme. Rainwater and greywater system products and components are
35
Environment Agency (2008). Water related infrastructure for sustainable communities: Technological Options and Scenarios for Infrastructure Systems. Science project SC050025. Environment Agency. Bristol
36 CIRIA (2001). Rainwater and Greywater Use in Buildings: best practice guidance (C539),
London.
37 Email communications (October 2010). Rainwater Harvesting Association
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 18 of 37 0845 600 8951
included on the Water Technology List38 and so capital allowances can be claimed on these
as well as for more standard water using fixtures and fittings.
6.2.2 Operating expense
Once in place, household rainwater systems will require investment to maintain operation.
Ongoing maintenance costs are estimated at around £50 per year, and pump replacement
will be required approximately once every ten years at a cost of around £200.
Over a 30-year accounting period the capital and operating costs have an estimated present
value of £2,300 and £930 respectively39. Inclusion of a rainwater system would not add
significantly to the costs of domestic electricity bills due to the relatively low energy
requirements for operating the pump (0.6kWh/m3). Entec has previously40 calculated the
present value of the additional annual energy cost required to run a rainwater system is £10
over a 30-year period using current prices.
Only customers with water meters will benefit financially from using a non-potable water
supply system. By October 2010 this applied to approximately 37 per cent of domestic
properties and almost all industrial and commercial customers. Therefore, in England and
Wales, for the majority of domestic customers, there is no financial incentive to install a non-
potable water supply system41. Suppliers of rainwater harvesting systems currently claim
savings of over 14 per cent of water used by the average household, but this still gives
payback periods well in excess of 10 years, based on the current unit cost of water and
wastewater services for domestic customers.
The financial situation is different for non-domestic premises as these are generally all
metered and the savings achieved, by rainwater harvesting systems in particular, will be
greater in larger buildings (such as industrial units and schools) due to their larger roof areas
and potentially greater demand.
Discussion with manufacturers has indicated that the non-household, new build, market has
increased quite significantly in the last few years. As that market has grown, the
technologies have improved, awareness has increased, and the costs have started to fall.
All of these factors may help to stimulate growth for rainwater and greywater systems in the
household market.
39 London Development Agency (2009). Managing Water - Reducing Water Demand. Technical Report (Entec, unpublished).
39 London Development Agency (2009). Managing Water - Reducing Water Demand. Technical Report (Entec, unpublished).
40 London Development Agency (2009). Managing Water - Reducing Water Demand. Technical Report (Entec, unpublished).
41 Environment Agency (2010). Harvesting rainwater for domestic uses: an information guide
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 19 of 37 0845 600 8951
6.3 Social factors influencing uptake of non-potable technologies
Studies by the Consumer Council for Water42 and the Environment Agency43 have shown
that few people think about their water services in the course of their everyday lives, and of
those that do, many underestimate the volume of water used in typical household tasks.
This presents a serious challenge to efforts to reduce demand, particularly for those wanting
to encourage the adoption of water efficiency measures within the wider consumer base (for
example, through retrofitting), but also highlights the opportunity and importance of building
low water use technologies into new developments. Water reuse technologies must meet
consumer expectations to deter users from reverting to 100 per cent supply from potable
mains supplies.
At present rainwater and greywater systems are not common in England and Wales. This
may be because:
Systems are expensive to purchase, maintain and run, while the cost of water is
relatively low;
Only 37 per cent of domestic customers have metered water supplies and thus would
save money;
Concerns that the quality of the water (particularly greywater) may pose a risk to
health. However, in 2007 the MTP carried out a review of rainwater and greywater
systems and made recommendations for quality guidelines and monitoring
arrangements44. The British Standards subsequently published guidance and
recommendations within BS 8515:2009 Rainwater Harvesting Systems: Code of
Practice, and BS 8525-1:2010 Greywater Systems Part 1: Code of Practice. These
standards are designed to ensure that reused water does not pose a risk to human
health; and
The reliability of greywater systems has been poor in the past and remains largely
unproven in terms of a mass market. It should be noted that rainwater harvesting
systems have also had a lot of reliability issues.
The health concerns are twofold: firstly, the health risk from contact with harvested or reused
water in the normal operation of the system and, secondly, the health risk posed by the
failure or ineffective operation of the treatment system. Greywater reuse systems are
designed to ensure that there is minimal user contact with the greywater. Aerosols from toilet
flushing are the only potential contact most users will have with the water and this is unlikely
to have health implications providing the manufacturer‟s maintenance procedures are
followed and the water has been properly treated.
42
Consumer Council for Water (2006) Using Water Wisely. 43
Environment Agency (2007e). Towards Water Neutrality in the Thames Gateway. Public acceptability of water efficiency scenarios. Science report: SC060100/SR2. Environment Agency. Bristol
44 Market Transformation Programme (MTP), Rainwater and Grey Water: Review of water quality standards and recommendations for the UK, www.mtprog.com
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 20 of 37 0845 600 8951
6.4 Opportunities for, and barriers, to the incorporation of
rainwater and greywater
6.4.1 Developers
The large scale housing development forecast by the Government45 creates an opportunity
to increase the number of households incorporating non-potable water supply systems. In
new developments, it may be possible to incorporate communal systems into large-scale
housing developments thus bringing economies of scale to the installation, performance and
maintenance of the systems. Such communal systems may include additional storage
capacity to provide stormwater control as part of a Sustainable drainage system (SUDS).
For larger scale systems, i.e. where greywater is discharged from households, the water
may be treated in the same way as sewerage using traditional biological methods combined
with modern filtration methods. Such a system may be combined with a sustainable
drainage system as a concept at a building‟s design stage rather than post construction
retrofit. The economy in both the reduction of water and sewerage charges may tip the
financial balance in favour of such a system.
The construction of high density mixed-use developments may limit the roof space available
per person to capture rainwater, whilst there may be insufficient rainfall to ensure that the
systems operate economically. Greywater systems do not have the same resource
limitations as rainwater systems since significant volumes of greywater will be generated.
The following information draws on previous work published by the Watersave network46 and
a recent feasibility study undertaken by the London Development Agency47. Table 6.2
highlights the opportunities and barriers to greywater reuse in new developments, rather
than existing homes. For example, the high capital costs to purchase the systems may deter
residents of existing properties from installing this technology. It should also be noted that
different stakeholders have different priorities regarding the opportunities and barriers
identified in Table 6.2.
45
http://www.communities.gov.uk/documents/statistics/pdf/1172133.pdf 46
Roaf, S. and Ghosh, S. (2002) Barriers and Drivers to Water Conservation and Recycling. Presentation to the Watersave Network. Presentation available from http://www.watersave.uk.net/Presentations/index.html and Baynes, S. (2002) Barriers to greywater recycling. Presentation to the Watersave Network. Presentation available from http://www.watersave.uk.net/Presentations/index.html.
47 London Development Agency (2009). Managing Water - Reducing Water Demand. Technical Report (Entec, unpublished).
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 21 of 37 0845 600 8951
Table 6.2 Opportunities and barriers to the incorporation of rainwater and greywater
into new developments
Category Opportunities Barriers
Physical Significant volumes of greywater will be
generated in new developments.
New developments allow systems to be
designed into the development at the build
stages.
Mixed use developments present
opportunities for domestic greywater to be
used in adjacent commercial or industrial
applications. Rainwater could be collected
from commercial roof space and used in
adjacent residential developments.
Space required for storage tanks may not be
available.
Roof area may be insufficient to generate sufficient
rain water to meet demand.
Rainfall availability in the London region.
Potential conflict with other policies, such as green
roofs.
Performance Performance of systems is improving based
on experiences of trial developments.
Opportunity to incorporate experience from
other countries to influence design and
system.
System reliability issues with greywater systems.
Maintenance requirements.
Economic Reduced water bills for the customer.
Economies of scale for rainwater and
greywater systems being introduced into
large developments at the communal scale.
Ongoing maintenance costs.
Requirements for a contractor to maintain the
systems.
Social - Unfamiliar technology.
Impact on lifestyle.
Requires commitment from householder to ensure
that system operates correctly.
Perception Opportunity to capitalise on the consumer‟s
“environmental stewardship”.
Homes meeting high standards of
environmental performance seen as “trendy”.
Recent drought events have highlighted water
scarcity as an issue.
Refusal or disgust at the concept of re-using water
used by other people.
Lack of perception of need for this technology amongst
the public.
Water seen as less important than other environmental
objectives such as energy use.
Legislation Level 5 and 6 of the CSH may require reuse or
harvesting technology.
No clear standards determined for water quality in
greywater and rainwater systems.
Environmental Potential to benefit other environmental
measures such as flood risk mitigation.
Reduction in mains water demand.
More concentrated sewage being returned to sewers.
Greater use of disinfectants in greywater systems.
Embodied energy and carbon within the product
materials (e.g. storage tanks), and operational use.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 22 of 37 0845 600 8951
6.4.2 Existing housing
Existing householders do not have the same drivers or opportunities as developers. An
existing home is not subject to the water efficiency standards set out in the Building
Regulations, and an existing homeowner is unlikely to benefit from retrofitting their home to
adhere to the Code for Sustainable Homes. They may reduce their energy and water bills
but compared to the capital cost of the system and taking account of the additional power
demands that may be associated with a non potable system, these savings are likely to be
small. This is especially true for water whilst the unit price of water is still relatively cheap.
The financial payback period for an existing homeowner may therefore be lengthy.
Similarly, an existing homeowner will not have the buying power and economy of scale that
developers have. Installing non-potable systems into existing household is a retrofit process.
The cost of design and labour is higher than in a new build, and perceptions of prohibitive
costs may deter potential homeowners. The financial savings that could be accrued for a
customer on a metered supply are currently much less than the cost of installing and
maintaining non-potable water supply technologies. Currently, the main driver for existing
houses is a desire to be „green‟ or a desire to pioneer a new technology.
While it is possible to introduce rainwater and/or greywater systems into existing buildings,
consideration at the planning stage can improve their effectiveness, make installation more
straightforward and reduce cost.
6.4.3 Non-domestic premises
The situation is different for non-domestic premises as these are generally all metered and
the savings achieved, by rainwater harvesting systems in particular, should be greater in
larger buildings (such as industrial units and schools) due to their larger roof areas and
potentially greater demand.
In non-domestic premises, rainwater may be used in many other areas of application as a
substitute for mains water (e.g. cleaning, process water, irrigation and humidification, fire–
fighting, toilet flushing etc). In addition, reclaimed water might be reused along with
rainwater in industrial applications (e.g. for cooling water, filter backwash water and some
process water).
Manufacturers have also reported that the need to comply with BREEAM has seen the
commercial market grow and has seen the inclusion of rainwater harvesting in large
numbers of new public type buildings (e.g. schools, colleges, prisons, health centres, and
fire stations)48.
48
Email communication (October 2010): Aquality Trading & Consulting Ltd.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 23 of 37 0845 600 8951
7 Sustainability of non-potable technologies
7.1 Energy and carbon
Water efficiency is seen as part of the solution to the increasing pressure on the water
environment, from growing population, increased demand, climate change, and increasingly
stringent environmental legislation seeking to reduce water abstraction in areas where
abstraction is causing environmental degradation. However, whilst water efficiency can be
seen as a positive step it may clash with other sustainability issues and environmental
considerations, most notably on carbon.
The Environment Agency greywater information guide49 shows that supplying a low flush
toilet with greywater requires approximately seven times the energy that is required when
using mains water. Embodied carbon within the materials used to manufacture and install
greywater and rainwater systems can be considerable, i.e. fibreglass/plastic tanks, and
concrete bases. The embodied carbon from infrastructure elements of rainwater systems
could be as much as 36 per cent of the total carbon dioxide equivalent impact of the system
over a 30 year lifespan50.
The carbon emissions that result from using a typical RWH system are, on average, around
40 per cent greater than emissions from using mains water. The evidence shows that
collecting, storing and pumping rainwater for domestic uses is not an energy saving
technology.
Over a 30-year lifetime the net emissions split of operational and embodied energy varies
considerably. Research shows that for an average 90m2 semi-detached house with 3
occupants the split is 52 per cent operational to 48 per cent embodied emissions, excluding
emissions from excavation and transport. This highlights that the carbon contribution from
embodied and operational emissions of a RWH system are both significant parts of a
system‟s total emissions.
Although rainwater and greywater systems do introduce additional energy demands for
pumping and treatment, it‟s important to put these emissions in context. The amount of
energy used by even the most complex reuse system is small compared with the energy
used to heat water in the home. Heating water for domestic uses, such as showering and
bathing currently contributes about five per cent of the UK‟s annual greenhouse gas
emissions51.
49
Environment Agency (2008c). Greywater: an information guide. Environment Agency. Bristol 50
Thornton. J. (2008) Rainwater harvesting systems – are they a green solution. In Green Building Magazine, Spring 2008 pp 32-35
51 BNWAT07: Water and Energy Use.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 24 of 37 0845 600 8951
8 Non-Potable Technology Innovation
Recent years have seen increased interest in „green‟ technologies and greywater reuse is no
exception52. Rainwater harvesting is on the increase in the UK and the UK Rainwater
Harvesting Association formed in 2004 in response to this. The Association now has 31 full
members, who are all UK companies. Research undertaken by Entec for the MTP update
included consultation with the Rainwater Harvesting Association and several specific
companies. It concluded that in the last three to five years there has been growth in the
number of companies providing these services, a direct response to the increase in demand.
Whilst some manufacturers have spent time developing more efficient products over the last
five years (since 2005), many of the systems available on the market have not changed. The
British Standard has seen a standardisation of design and components and, coupled with
BREEAM, has ensured that system sizes are, in the main, fit for the intended purpose53.
Use of rainwater harvesting is increasing in Japan, Australia and Germany, and is more
widespread in these countries than in England and Wales. In Japan planning regulations
require that buildings with a floor area greater than 30,000m2 have rainwater harvesting
installed, while in Belgium buildings with roof area greater than 100 m2 are required to have
combined rainwater harvesting and stormwater attenuation systems. In Germany around
1.5 million homes and workplaces have rainwater systems installed54.
Similarly, greywater reuse systems are not as common in England and Wales as they are in
some other countries. One drawback to greywater reuse is the potential for health
implications if systems prove unreliable. Other countries are dealing with this in different
ways. For example in Japan, only washbasin water is used to flush household toilets. On a
wider scale however, the Japanese reclaim wastewater to flush toilets, for irrigation, and for
use in ornamental ponds/fountains. This happens in high rise buildings and at regional
treatment plants. The processes are sophisticated and expensive but because of Japan‟s
severe water shortage, it is economical55.
Specific regulations and requirements for treating and using greywater vary between
countries and states. However, countries with severe water shortages have identified the
best technical approach for them and encouraged uptake through incentive programmes.
For example, the Australian Government offers A$500 rebates for the installation of a
greywater system. Several municipalities of Spain, including Sant Cugat Del Vallès near
Barcelona and several other municipalities in Catalonia, have also passed regulations to
52
Environment Agency (2008). Greywater: an information guide. 53
Email communication (October 2010). 54
Environment Agency (2010). Harvesting rainwater for domestic uses: an information guide. Environment Agency. Bristol
55 Australian Water Research Foundation. Domestic Greywater Reuse: Overseas Practice and its
Applicability to Australia. http://www.fwr.org/wsaa/wsaa73.htm
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 25 of 37 0845 600 8951
promote greywater reuse in multi-storey buildings56. Other countries also have incentive
programs for installation of greywater systems, including Korea and Cyprus57.
8.1 Integrated rainwater and greywater systems
Integrated systems include both rainwater harvesting and greywater reuse systems. Factors
that influence the success of such systems include the amount of rainfall available, the size
of catchment areas (i.e. roof catchments/hard-standing areas) and the number of people
living within the development. There are examples of these systems being employed in
other countries such as Japan, where the installation of such technology is considered
routine. The Roppongi Hill development in central Tokyo is a mixed use development of
residential, retail, hotel and business units, where a large scale system of greywater and
rainwater reuse is in place. Around 43 per cent of water use across the development is
provided from these sources58.
Within England and Wales there are examples of integrated systems, which capture
rainwater and recycle greywater within a development. The objective of such systems is to
make a development self-sufficient. Two examples from England and Wales are the
ecological Hockerton Housing Development, Nottinghamshire59, UK and the Childwall Estate
Redevelopment in Liverpool60. There are drainage implications for integrated systems.
Normally all overflows discharge to the foul sewer network as the two non-potable sources
may be mixed in the same tank. This means that the water is not of sufficiently good quality
to be discharged into water courses. It may be possible for a combined system to have an
overflow into storm drain, but only if it is guaranteed that the rainwater will not be mixed with
greywater when overflowing. This may involve using a diverter valve.
56
Domenech, L. and D. Sauri. (2010). Socio-technical transitions in water scarcity contexts: Public
acceptance of greywater reuse technologies in the Metropolitan Area of Barcelona. Resources,
Conservation and Recycling Volume 55, Issue 1, November 2010, Pages 53-62.
http://www.sciencedirect.com/ 57
Canadian Water and Wastewater Association. (CWWA). (2002). Research Highlights: Rainwater Harvesting and Grey Water Reuse. Technical series 03-100. http://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/03-100-e.htm.
58 Greater London Authority (2007) Water matters. The Mayor‟s Draft Water Strategy Draft for consultation with the London Assembly and functional bodies. GLA. London.
59 www.hockertonhousingproject.org.uk and Environment Agency (2010). Harvesting rainwater for domestic uses: an information guide
60 joint winner in the 2004 Sustainable New Homes Awards
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 26 of 37 0845 600 8951
Recommendations – Action plans
8.2 Actions to achieve increased use of non-potable water supply
systems
Local and national programmes to support the expansion of rainwater harvesting /
greywater reuse systems could increase uptake. It is recommended that the
Department for Communities and Local Government review planning policy and
guidance that strongly encourages rainwater and greywater systems in new
development. These policies could be targeted at areas where the water savings and
wider benefits would be of most value61, for instance in London and the South East.
Local Planning Authorities should be encouraged by the Government to incorporate
the new guidance in their Core Strategies to increase uptake of rainwater and/or
greywater systems, in developments that are suitable in their local area. Alternatively,
these requirements could be brought into policy through Local Authority
Supplementary Planning Documents. In 2009 the London Development Agency (LDA)
commissioned a study to better understand if non potable supplies were feasible in
different types of building within London62. It is recommended that other Planning
Authorities follow this example to understand the opportunities, costs, and benefits of
bringing these non potable systems into mainstream planning.
The feasibility of rainwater harvesting and greywater reuse, together with sustainable
drainage systems, should be assessed in the earliest possible stages of development.
The most effective way to ensure that non-potable systems are planned and designed
from the outset is for the construction client to specify this in their original brief. The
likelihood of this happening will increase if Local Planning Authorities include a
requirement for feasible non-potable systems in their planning policies. The planning
process needs to be flexible enough to recognise that non potable systems are not
feasible in every situation.
The Government (for example CLG) should seek opportunities to work directly with the
major development companies to research and produce guidance that will support
developer portfolios including non potable systems as standard, where feasible.
Central and Local Government should work together with developers to share
knowledge on how (and whether) rainwater systems can be integrated within surface
water management plans for new developments, particularly for sites that are subject
to strict surface runoff criteria.
61
Environment Agency (2010). Energy and carbon implications of rainwater harvesting and
greywater recycling. 62
London Development Agency (2009). Managing Water - Reducing Water Demand. Technical
Report (Entec, unpublished).
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 27 of 37 0845 600 8951
Maintenance of non-potable systems is a perceived barrier to uptake. Government
should facilitate discussion between developers and systems manufacturers to better
understand the actual maintenance requirements of different systems so that
appropriate long terms maintenance plans can be developed and agreed where these
systems are being fitted.
The Government should promote the ECA tax relief on rainwater harvesting systems.
Greywater reuse systems do not attract the ECA benefit of rainwater systems;
however, their installation and use can still reduce both the demand for wholesome
water and drainage discharge. At present, their installation as a retrofit together with
their frequent maintenance requirements suggest that any financial saving will be
small, leading to a long payback period. Although greywater systems have the
potential to save up to 30 per cent of water, a number of issues need to be resolved,
including the return to sewer charges, before greywater systems are widely accepted.
It is important to continue to educate and engage customers in water efficient
behaviours and to tackle the perceptions surrounding the feasibility and acceptability of
rainwater harvesting and greywater reuse. Water companies have a key role and
opportunity to issue information to their customers on water resources and the need to
conserve water. Many people still believe that it is not necessary to be water efficient
in England and Wales because there is plenty of rain. People need to become more
familiar and comfortable with these technologies and so public buildings that have
them installed should advertise this more.
The MTP should support and encourage the water companies who are actively
involved in educational activities to promote alternative sources of water, such as
rainwater butts for home use and the cost saving potential of greywater and rainwater
systems.
Various incentives could be considered to increase appropriate uptake, as seen in
other countries. Options include:
Financial incentives:
- Subsidising the installation (rebate);
- Purchase tax incentive (lower VAT);
- Council tax incentive (lower rateable value);
- Lower water charges;
- Higher stamp duty threshold for homes with an alternative water supply; and
- Code for Sustainable Homes.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 28 of 37 0845 600 8951
Whilst some of these options may not appear feasible in the current economic climate
(2011), they should be considered, and not dismissed as unrealistic.
Public attitudes towards harvested rainwater and greywater are important for their uptake.
Studies have shown that there is generally a positive attitude to the use of recycled water for
toilet flushing63 but that with more “personal” uses e.g. garden watering, the acceptability
decreases. In communal reuse schemes studies have found that users prefer to reuse their
own greywater rather than someone else‟s64. Research suggests that where communal
systems are installed, people prefer larger „city wide‟ schemes where the source of the water
is anonymous rather than local schemes where they may know many of the people
involved65.
8.3 Actions to resolve outstanding data gaps or other issues
The Environment Agency report examining the „Energy and carbon implications of
rainwater harvesting and greywater reuse‟ presents the carbon footprint of water
supplied by „non-potable‟ systems compared to mains water. However, more
information is required on the likely energy costs to the homeowner of running a
greywater or rainwater system. If the energy costs are too high to the customer, this
may exceed the saving on water bills.
Both the rainwater and greywater reuse British Standards have embedded water
quality parameters for water reuse applications to ensure public health is not
compromised. This is the first time that water quality requirements have been included
and should set a precedent that water quality is a mandatory expectation.
63
Hills, S., Birks, R., and McKenzie, B. (2002a). The Millennium Dome “Watercycle” Experiment: to evaluate water efficiency and customer perception at a recycling scheme for 6 million visitors. Wat. Sci. Tech., 46(6–7), 233–240; and Ogoshi, M., Suzuki, Y. and Asano, T. (2001) Water reuse in Japan. Wat. Sci. Tech., 43(10), 17–23.
64 Jeffrey, P, 2002 Public attitudes to in-house water recycling in England and Wales, Journal
of the Chartered Institution of Water and Environmental Management, 16, 214-217. 65
Po, M, Kaercher J D and Nancarrow B E, 2003 Literature Review of Factors Influencing Public Perceptions of Water Reuse. CSIRO Land and Water, Technical Report 54/03. http://www.clw.csiro.au/publications/technical2003/tr54-03.pdf
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 29 of 37 0845 600 8951
Appendix A
Product descriptions
A.1 Rainwater harvesting
There are three basic types of rainwater harvesting systems66:
Water collected in storage tank(s) (i.e. at ground level or underground) and pumped
directly to the points of use;
Water collected in storage tank(s) (i.e. in roof spaces) and fed by gravity to the points
of use; and
Water collected in storage tank(s) (i.e. at ground level/underground), pumped to an
elevated cistern and fed by gravity to the points of use.
Within these basic types, there are variations such as:
Internal or external locations for tanks;
Single or multiple linked tanks;
Freestanding or fully buried or partially buried tanks;
Communal tanks supplying multiple properties; and
Packaged systems or components.
Rainwater collection area/rainfall/storage
Rainwater may be harvested from roofs and hard-standing, such as driveways and can
either be stored underground or in roof spaces. Storage in the roof space enables flow to
fixtures such as WCs to be via gravity, however this option is generally ruled out because of
limited space (and therefore storage) and the implications that additional loading from a
large water tank has on construction design, methods, materials and cost. These factors
mean that conventional household rainwater systems generally have underground storage
tanks located adjacent to the property, e.g. underneath the rear garden.
The roof or catchment area for collecting rainwater, the average annual rainfall and
distribution through the year and materials the roof or catchment area are constructed from
will determine the available yield of rainfall. Local rainfall data may be available from the
Environment Agency or the Met Office. For domestic application, rainwater storage tanks
are commonly sized at 5 per cent (0.05) (This represents 5 per cent of the year (18 days) of
the rainwater supply or of annual demand, using the smallest of the figures.
66
BS 8515: 2009. Rainwater harvesting systems – Code of practice.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 30 of 37 0845 600 8951
The size of tank needs to be large enough to maximize the use of rainwater during dry
periods, but to allow overflow at least twice per year to flush out debris. More detailed
calculation methods are given in CIRIA guidance67.
When calculating yield, the total „catchment area‟ should take account of both: roof area in
m2 and; if used, the runoff water from a hard-standing area into a sustainable drainage
system. A drainage coefficient (runoff factor) is used to adjust the efficiency of collection
and, therefore, the required size of tank. Filter efficiency will also have an effect on the
harvested quantity.
Tanks should be located to avoid extremes of temperature, as higher temperatures could
encourage bacterial growth in the stored water, and freezing conditions can damage the
tank. Tanks tend to be stored underground, and sufficient space needs to be available in the
development layout. A typical tank volume for a single household is 1.0 to 3.0 m3.
Rainwater pumping mechanisms
Rainwater is usually pumped from the underground storage tank to a header tank located at
high level. A similar arrangement is commonly used for greywater. In the event that the
alternative water supply cannot meet demand though lack of rain or pump failure, mains
water must be available to top up the tank via a required type AA air gap. Some appliances
can be adapted for a connection to both wholesome and a non-wholesome water supply
(e.g. a WC cistern may be adapted for dual feed, provided that a type AA air gap is provided
to prevent mains water contamination). The rainwater supply pump can either be a
submerged unit in the main storage tank, or a suction pump outside it.
Suction pumps are usually located within the control unit and must be positioned relatively
close to the tank, in frost-free conditions. Automatic sensors are usually used to activate the
pumps to replenish the header tank or directly refill a WC cistern.
Sensors to protect pumps from dry running should also be considered. Filters are the first
line of treatment, initially preventing solid debris from entering the holding tank. Finer
downstream filters may be required depending on the uses to which the alternative water
supply is to be put.
All pipe-work carrying non-wholesome water must be clearly marked. All installations must
comply with the Water Regulations.
Individual or shared systems
Rainwater harvesting can be installed for individual households, or on a larger scale where
water is collected from a number of properties (for example in a street), treated centrally then
pumped to individual households for reuse.
67
CIRIA (2001) Rainwater and Greywater Use in Buildings: Best Practice Guidance. Report C539. CIRIA, London
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 31 of 37 0845 600 8951
The benefits are savings in potable water use and discharge rates to sewers, and reduced
runoff rates and consequent risk of surface water flooding from new developments.
Planning policy now requires that sustainable drainage systems are used in new
developments where possible to reduce flood risk, and rainwater harvesting can contribute
to sustainable drainage design68.
Advantages of a centralised system over single household units may include that:
Water is collected from areas of hard-standing within the development, for example
walkways and paved areas, which increases the volumes collected for re use; however
water collected from these areas may need more treatment, to remove pollutants from
roads, compared to water collected only from roofs;
Collecting rainwater from paved communal areas will reduce rainfall runoff further;
The system is likely to be maintained by qualified personnel (e.g. a service contractor)
rather than individual householders;
There will be cost savings in installing large communal systems (due to economies of
scale) compared with installing individual households covered by the communal
system.
However, there may be a user perception that they don‟t want to use communally collected
water.
Rainwater harvesting systems need to be maintained and if single household units are
installed the householders will be responsible for this. BS 8515 recommends checks once
per year, but filters may need cleaning more often and gutters need to be kept free from
debris. The mains back-up should be checked once per year for correct functioning. Hence
these are not (and never will be) fit-and-forget systems, and house owners/occupiers will
need a level of commitment to keep them operating.
Where communal systems are installed a contractor will need to be employed to maintain
the system, and the costs of responsibility and payment for maintenance should be
considered early in design phase of any system. Options include charging residents of a
development a maintenance fee for the upkeep of the system. This is likely to be relatively
straightforward in social housing developments, where maintenance costs could be collected
and administered by the organisation responsible for the housing (e.g. a housing
association). In private developments a maintenance contract may need to be agreed on
purchase of the property, with maintenance being administered by a private company.
68
Communities and Local Government (2006) Planning Policy Statement 25: Development and Flood
Risk. Communities and Local Government. Wetherby.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 32 of 37 0845 600 8951
A.2 Greywater reuse
Greywater reuse systems vary significantly in their complexity and size from small systems
with very simple treatment to large systems with complex treatment processes. However,
most have common features such as:
A tank for storing the treated water;
A pump;
Water treatment; and
A distribution system for transporting the treated water to where it is needed.
All systems that store greywater have to incorporate some level of treatment, as untreated
greywater deteriorates rapidly in storage. The tank should also incorporate a mains water
connection for when supply does not meet demand and this must include backflow
protection, in order to comply with the Water Supply (Water Fittings) Regulations 1999 and
prevent contamination of the mains supply.
Types of greywater system
A recent Environment Agency report69 recognises five broad types of greywater systems:
Direct reuse systems;
Short retention systems;
Basic physical and chemical treatment systems;
Biological treatment systems; and
Biomechanical systems.
Direct re-use systems include storage of very short duration. This could include using
water from kitchen sinks or baths directly in the garden. This does not require advanced
technology (a bucket or a siphon hose can be used), and items such as the Watergreen70
have been developed to facilitate this. This simple approach of using a siphon hose is a
short term measure (marketed as a drought measures) and is not a fit and forget technology
suitable for inclusion in new developments.
Short retention greywater systems, such as Ecoplay71 use settlement or skimming
technology to remove materials from greywater, but do not provide any further treatment.
When untreated greywater is retained, even for short periods, bacteria can build up causing
69
Environment Agency (2008). Greywater: an information guide. Environment Agency. Bristol 70
www.droughtbuster.co.uk 71
http://www.ecoplay-systems.com . Other systems are available.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 33 of 37 0845 600 8951
odour and water quality issues. It is, therefore, undesirable to have a large storage tank.
Short retention systems release unused greywater from storage to waste to avoid these
problems. Mains water is then used in its place. The collection/holding tank for grey/
recycled water should be positioned in a relatively cool but frost-free environment to
minimise bacterial growth.
Basic physical and chemical systems provide simple filtration and chemical disinfection
treatment to greywater. This enables more greywater to be stored for longer periods of time
and thus offer a greater potential for minimising demand in new developments. The systems
require more storage space for tanks than short retention systems due to the volume of
greywater that can be stored. Provision for the storage tank will need to be incorporated into
the design of a building for individual property systems. Storage tanks are normally located
outside the building either buried within the garden or as an above ground tank, similar in
appearance to a water butt. Greywater collects in the storage tanks and is pumped to a
header tank located within the roof space of a property. The water is then supplied via
internal plumbing, usually for the purposes of toilet flushing.
Biological treatment systems, such as the Green Roof Water Recycling System, GROW72,
use naturally occurring bacteria to treat greywater. By employing such processes a
biological greywater system is essentially performing the same functions as an on-site
sewage treatment works. The most common form of biological treatment is passing
greywater through reed-beds where bacteria in the plant root systems break down organic
waste using oxygen supplied by plants. This is a well established method for treating
wastewater, and reed-beds can provide amenity and ecology value, although they do require
relatively large areas of land. For this reason they may not be suitable for some new
developments in the highly urbanised areas.
Bio-mechanical systems are the most advanced greywater treatment systems and perform
similar functions to an on-site sewage treatment works. An example system is the Pontos
Aquacycle73, which filters greywater from baths and showers before a two stage treatment
process of where micro-organisms break down organic material. The partially treated water
is then settled and disinfected with ultraviolet light. The manufactures claim that the treated
water is suitable for use in toilet flushing, washing machines, cleaning and garden watering.
The Aquacycle technology is available for application at different scales, with single
domestic units such as the Aquacycle 900 to the AquaCycle 13,500 with a 13,500 litres/day
capacity, suitable for development level installation or use in larger commercial properties.
It is the basic physical and chemical treatment systems that have been most widely applied
in trials in the UK at the individual household level. Findings have been published from a
number of trial studies such as a national trial by the Environment Agency74, and a study by
72
http://www.wwuk.co.uk/grow.htm 73
www.ribaproductselector .com/docs/1/11501/external/COL311501.pdf?ac= 74
Environment Agency (2000) A study of domestic greywater recycling. Environment Agency. Worthing.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 34 of 37 0845 600 8951
Cranfield University and Thames Water in Aylesbury75. Most studies report technical issues
relating to the reliability of the systems and the quality of greywater captured.
There are also issues relating to public perception of greywater reuse and the performance
of the systems impacting on the residents in households where such systems have been
installed that many would deem unacceptable. Few of the individual greywater systems that
have been trialled within the UK have collected water from the kitchen due to the presence
of fats within the wastewater stream. These can collect and block the filter systems76.
Greywater systems can be implemented at the individual property level or as communal
systems at the development level. At the individual property level, there are concerns over
the reliability and performance of systems. The issues are likely to be minimised if
greywater systems are implemented at the communal level, since established treatment
technologies akin to those that are tried and tested in sewage treatment processes could be
implemented. However, there could still be issues of resident acceptability over the concept
of using other residents treated wastewater that may prove a barrier to implementation in
new developments.
A.3 Maintenance
An alternative water supply is not a „fit and forget‟ technology, maintenance schedules must
be adhered to in order to keep a system running correctly and avoid bacterial growth and
contamination. Maintenance should, therefore, include:
General cleaning and maintenance of rainwater collection areas;
Removal of debris that could block a system;
Annual visual inspection of the system components;
Cleaning/replacement of filters in accordance with the manufacturer‟s
recommendations;
Regular checks on greywater disinfection in accordance with the manufacturer‟s
recommendations; and
Checks that the mains water top-up is functioning
75
Jeffrey, P. (2005) Assessment of water savings from single house domestic greywater recycling systems, IWA 2nd International Conference on Efficient Use and Management of Water in Urban Areas, held in Tenerife, Canary Islands, 2004. ISBN: 1843394669. IWA Publishing.
76 Environment Agency (2000) A study of domestic greywater recycling. Environment Agency.
Worthing.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 35 of 37 0845 600 8951
Appendix B
Environmental benefits
B.1 Reduced water consumption
In the short term, water conservation devices and water efficient products offer greater
financial and water saving benefits. However, in the longer term, the financial and
environmental benefits for the water-stressed areas of England and Wales may well shift the
balance in favour of alternative water supplies.
B.2 Reduced energy consumption
There are three primary areas of energy use with regard to water:
Energy embodied energy in the water supplied;
Energy used to heat domestic hot water and for central heating; and
Energy used in appliances (e.g. dishwashers, washing machines, shower pumps).
Rainwater and greywater systems avoid using the embodied carbon in potable water, but
they have their own carbon footprints which vary depending on system type, installation
arrangements, and the level of demand. Pumping requirements are the main factor.
Greywater also has on-site treatment issues such as the release of chemicals/disinfectants
into the foul drainage system.
B.3 Support sustainable drainage
Rainwater systems reduce the volume of rainwater that drains directly from buildings. The
water will be released at a slower steady rate as dictated by flushing frequency, and passes
into the foul sewerage system, rather than surface water drains (for new developments, at
least).
In addition to the strain on water resources, there are also concerns about rainwater
drainage from urban areas. Planning authorities are required to consider the effects of
surface water drainage and the potential impact on flood risk, (in England, Planning Policy
Statement (PPS25)). This means that traditional combined sewerage approaches are no
longer acceptable in new developments. Rainwater harvesting can contribute to an overall
approach to sustainable urban drainage systems (SUDS).
For a larger scale system, greywater may be treated in the same way as sewerage using
traditional biological methods combined with modern filtration methods. Such a system may
be combined with a sustainable drainage system as a concept at a building‟s design stage
rather than post construction retrofit. The economy in both the reduction of water and
sewerage charges may tip the financial balance in favour of such a system.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 36 of 37 0845 600 8951
Reclaimed water systems can play a part in water conservation by reducing the amount of
mains supplied water used in the home and non-domestic buildings. However, it is vital to
ensure that the design, installation and maintenance of such systems do not compromise
public health by contamination of the wholesome mains water supply through inadvertent
cross-connection or backflow. Installations must, therefore, comply with the Water Supply
(Water Fittings) Regulations 1999 in England and Wales and Approved Document H of the
Building Regulations.
Version: 1.0
First created: 11/03/2011
Updated: http://efficient-products.defra.gov.uk
Last reviewed: 11/03/2011 37 of 37 0845 600 8951
Related MTP information
MTP (2007). Rainwater and Greywater: review of water quality standards and
recommendations for the UK
MTP (2007). Rainwater and Greywater: technical and economic feasibility
MTP (2007). Rainwater and Greywater: a guide for specifiers
Changes from earlier version
This briefing note replaces the following previous briefing notes:
BNWAT19: Alternative sources of water – greywater and rainwater reuse: Innovation
briefing note
Consultation and further information
Stakeholders are encouraged to review this document and provide suggestions that may
improve the quality of information provided. Email [email protected] quoting the
document reference, or call the MTP enquiry line on +44 (0) 845 600 8951.
For further information on related issues visit http://efficient-products.defra.gov.uk