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Rainwater Harvesting InThe Sustainable Environment

Polypipe Continuing Professional Development

Introduction to Polypipe Terrain

Aims and Objectives

The Sustainable Environment

The Concept of Rainwater Harvesting

Legislative Changes & Drivers

The System

Maintenance Requirements

Life Cycle Costs

Summary & Conclusion

Open Forum

The Sustainable Environmental

Flooding as a result of extreme storms similar to those of the summer 2007:

57,000 homes were affected by surface water flooding Damage estimated to be around 3 billion Currently 80,000 homes in the UK have a 10% annual chance of

suffering surface water flooding with the likelihood of damages estimated at 270 million per annum.

The Sustainable Environment Climate Change is driving the need for innovative solutions for surface water

management

Average UK annual temperatures may rise by 2 3.5C by the 2080s

Seasonal distribution of rainfall will change significantly with the possibility of winters becoming wetter.

Sea levels are expected to rise by between 90 to 690 mm

Increase in the prevalence of extreme weather events


Exceptionally low rainfallSubstantially below averageBelow averageNormal rangeAbove averageSubstantially above averageVery Wet

With the exception of the South West,the whole of the UK has seen aboveaverage rainfall compared with the

1961 1990 average

Source Met Office


(Environment Agency 2007)

For most companies (Water Supply Undertakers), the largest component of increased demand is customer water consumption; in other words it predicted that we will nearly all use more water in our homes in the next 25 years.

ModerateSerious

Low

The water stress method takes a long-term view of the balance between water availability and thedemand for public water supply, rather than a snapshot of shorter or peak periods.


Natural Undeveloped Land

95% 5%

Developed Land

5%95%


Potable water is not as abundant in England and Wales as you would think. We only have 1,334 cubic metres (m3) per person a year much less than France (3,065 m3) or even the hotter Mediterranean countries of Italy (2,785 m3) and Spain (2,775 m3). South East England has even less water per person due to its high population density. The Thames Valley has only 266m3, only a fifth of the England and Wales average.

The average person in England and Wales uses 150 litres of water every day. Most of it is used for washing and toilet flushing, but it also includes drinking, cooking, car washing and watering the garden. We use almost 50% more water than 25 years ago.

Source OFFWAT

For most companies (Water Supply Undertakers), the largest component of increased demand is customer water consumption; in other words it predicted that we will nearly all use more water in our homes in the next 25 years.

Environment Agency - 1998


Domestic Water Consumption

Commercial Water Consumption

Market Sectors

Housing Commercial / Industrial / Retail Agricultural / Animal Shelters Education Leisure Utilities Ministry of Defence Hospitals Fire, Police and Ambulance Stations Airports

Rainwater Harvesting Applications

Housing

Speculative

Self Build

Social


Commercial / Industrial / Retail

Retail

Commercial

Industrial

Agricultural / Animal Shelters

Organic Farming

Horticulture

Animal Husbandry

Animal Sanctuaries



Educational

Universities

Secondary Schools

Primary Schools


Leisure

Golf Clubs

Swimming Pools

Football Stadia

Assessment Criteria

Principal use and location Roof area Roof Construction Number of occupants Applications for rainwater Peak and total water demand Gravity or pressurised system Rainfall data Water supplier Detailed requirements Health and Safety considerations

Assessment

Basic Information Requirement

To allow even a budget specification and quotation to be prepared for the client, the following information will be required

Site Location This will allow us to use the correct rainfall average and will also define the water company in the area thus allowing us to calculate the water cost saving.

Roof Area & Material The surface area of the roof used for harvesting purposes is required.

Drainage System Used Commercial roofs will either have standard gravity downpipes or siphonic downpipes. Siphonic systems will increase the flow rate thus affecting the filter chosen

Assessment

Type of Site Is the site a school, an office, domestic housing, industrial etc

Population on site Split in to Male & Female. How many of each on site.

Site Hours of Use How many hours per day, how many days per week etc

Use for Water Toilets, irrigation, vehicle washing, industrial etc If non standard use, try to find out quantity used.

Delivery of Water How will the water be delivered to the appliances? Via a header tank, a booster set or direct to appliances.

Pump Duties Rarely available at this stage. Pumping distance. Flow requirement. Pressure requirement. Pipe work size etc.

Legislation, Regulations & Drivers

British Standards BS 8515:2009British Standards BS 8515:2009 Now seen as the definitive guide for Rainwater Harvesting

design

Public Health considerations Document L8

BREEAM

Water Supply Regulations Building Regulations considerations

Important References

Part H of The Building Regulations

Planning Policy Guidance Note PPS 25

WRAS Information and Guidance Notes

The Private Water Supply Regulations

The Water Supply (Water Fittings) Regulations HSC Document L8 for the control of Legionella

CIRIA Notes C359 & PR080

Delayed Part G of The Building Regulations

Legislation

British Standard BS-8515:2009

In 2002 Approved Document H changed the hierarchy of drainage and drainage design considerably

Consider rainwater harvesting first and foremost Attenuation or if ground conditions permit, a soak away structure may be

used Discharge to sewer or watercourse may only be considered as a last

resort

PPS 25 -the EA to have a wider consultation role and recommends upsizing drainage by over 20% to cope with future building and climate change.

2008 Government Future Water Strategy launched together with a consultation on improving surface water drainage

2009 Water Framework Directive starts to be implemented

Future Water Strategy

Sets out how Government wants the water sector to look by 2030 with the following main aims :

reduced water demand by reducing average per capita water consumption from 150l/p/d to 120l/p/d

Improved water supply with more reservoirs and fewer abstractionlicenses Encourages rain water harvesting

Improve water quality in the natural environment Water Framework Directive (2009).

Improve surface water drainage by implementing SUDs Reduce flooding risk from rivers and coasts by more integrated strategic

planning Near universal water metering in water stressed areas Code for Sustainable Homes BREEAM

Concepts of Rainwater Harvesting

Rainwater Harvesting

Rainwater harvesting systems collect run-off from a roof and stores the rainwater in an appropriately sized tank.

Water is then pumped back into the building for use in non-potable applications such as toilet flushing, urinal flushing and commercial wash down areas.

Surface water from car-park areas can also be collected with rainwater only with a purpose designed treatment filter is used for the surface water

On average, 63% of the water used within a commercial building is not required to be of a potable standard and therefore rainwater can be used in these applications.

Gravity System

Captured water is pumped from the primary storage tank to a header tank at high level within the building

Water in the header tank is distributed to the point of use via gravity

Pump option to boost the supply to particularly remote outlets

Mains water top up directly to the header tank

Available in single and duty standby pump arrangements

Back up function ensures that water supply is maintained even in the event of power failure

Pressurised System

Electronic control system monitors demand for water

Water is pumped directly from the main storage tank directly to the point of use

The control system measures water level in the tank and imports mains water if required to prevent the system running dry

Delivers water under greater pressure

Space saving no need for header tank

Available in single and duty standby pump arrangements

Filtration

A Rainwater Harvesting System usually incorporates 3 forms of filtration

Pre-tank filter (leaf filter) Floating filter on the pump

In-line filter within the property

A fourth form of filtration will be incorporated if the system installed includes UV Disinfection.

All filters within the system should be cleaned regularly in accordance with manufacturers instructions

System Components

FILTERS

As stated in BS8515, filters must

Be water and weather resistant

Removable and accessible for maintenance purposes

Have an efficiency rating of at least 90%

Pass a maximum particle size of less than 1.25mm

All filters must conform to these specifications even sedimentation chambers

Pre-Tank Filters

Filter options for a widerange of internal and external applications

Calculating Tank Size

As stated in BS:8515 there are 3 different calculation methods Simplified Approach Intermediate Approach Detailed Approach

Simplified Approach Usually used for domestic dwellings and is based on roof area/annual rainfall/no of inhabitants

Intermediate Approach A little more in depth, with set equations used to calculate tank sizes based on either available yield or demand

Detailed Approach Used to calculate storage size more accurately when, demand is irregular, yield is uncertain or costly or larger rainwater harvesting systems are proposed

Usually all calculations are based upon storing 5% of annual rainfall (18 days)

DREAM Assessment Method calculates RWH tank sizes on 14 days and NOT 18!

Calculating Tank Size from available yield

We would in normal circumstances use the Intermediate approach

Yr = A x e x h x n x 0.05 (18/365) Where

Yr = annual rainwater yield (L) A = collecting area in m2

e = yield co-efficient (%) h = the depth of annual rainfall in mm

n = hydraulic filter efficiency (%)

Calculating Tank Size - demand

Tanks should be sized based upon 5% of the annual demand

Dn = Pd x n x 365 x 0.05

Where

Dn = annual non-potable demand

Pd = the daily requirement per person

n = number of persons

BOTH of the above calculations are outlined in BREEAM

Calculation constants & variables

Yield or roof co-effientPitched

BS:8515 states between 0.7 - 0.8 BREEAM States between 0.75 0.9Flat

BS:8515 no guidance BREEAM between 0.4 0.5

Green/Sedum Roofs No guidance in either generally taken as 0.4 as no other information is

available

Variations above are due to different roof materials

Calculation constants & variables

Filter efficiency is taken as 90% - co-efficient of 0.9

Annual Rainfall Data taken from Met Office based on published Regional variances

Storage 5% of annual yield 18/365 days 5% of annual demand 18/365 days This may differ when using the Detailed approach

Daily demand/requirement per person is dependant on No of people Flush volume Toilet visits Sex

System Components - Tanks

Domestic tanks usually from 1,500 litres to 6000 litres

Commercial tanks from 7,000 litres to 300,000 litres

Commercial GRP tanks in standard, medium & heavy duty depth based on application and water table

Concrete Tanks

Plastic tanks now available in larger sizes

Above Ground Tank Options

Sectional GRP Tanks

Internal plant room applications

Sizes from 1m3 to 100m3

Specialist erection on site

WRAS Approved

Insulated with 40mm polyurethane

Used in conjunction with pump booster set or combined control units

Typical system

Components

Pump

Floating filter

Inline filter

Controller

Combined Systems

System Components

Post Installation Inspection

Commissioning is the final stage when the system is shown to be functioning properly and is ready to hand over to the customer.

In order to ensure that the system is going to work properly the developer must ensure that :-

No debris is left inside the tanks or pipe work The system has been pressure tested and is watertight

Filters are correctly housed The level sensor is correctly positioned Warning gauges are correctly calibrated

The pump is correctly suspended (if it is in the tank) The control panel is working with all components The valves are working properly The mains back-up valve is working The system operates correctly in all actions at full pressure with no leaks or

weeps.

Ultra-Violet Disinfection Unit

BS8515 states that UV Disinfection for toilet flushing alone is not a standard requirement

Systems that generate water vapour or mist should be treated

Neutralises a wide range of bacteria including Legionella

Design restricts shadowingensuring optimum treatment efficiency

Wide range of units available

Regular maintenance is essential

Typical Pressurised System Layout

Gravity System

Combined Pressurised SystemsBelow Ground Option

Gravity System

Tanks and overflow

Pipe Identification

Life Cycle Costs

Rapid payback periods

Reduced investment requirements

Minimum 25 year design life

Low operating costs, typically 3p per cubic metre delivered

ECA Enhanced Capital Allowance


Leaf Filter

Tank

Components

U V Filter

The safe integration of this technology into our everyday working, living and sustainable environment


The Concept of Rainwater Harvesting

Legislative Changes & Drivers

The System


Life Cycle Costs

Summary & Conclusion

Open Forum

Summary and Conclusion

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