rainwater harvesting course 6 1 teacher saroj sharma s.sharma@unesco-ihe.org

RAINWATER HARVESTINGCourse 6

Teacher

Saroj Sharmas.sharma@unesco-ihe.org

About Saroj Sharma

Saroj Kumar Sharma graduated in Civil Engineering with distinction in 1988 (M.R.Engineering College, University of Rajasthan, India), completed his MSc in Sanitary Engineering with distinction in 1997 (IHE Delft, The Netherlands) and PhD in Groundwater Treatment in 2001 (Wageningen University and IHE Delft, The Netherlands). He is specialized in water supply engineering - water quality, treatment and distribution.

He has 22 years of professional and academic experience in planning, design, implementation, and operation and maintenance of urban, semi-urban and community-based rural water supply projects. He has worked with several government agencies, international consultants and donors (UNICEF, WHO, ADB, WB) in various water supply projects in different parts of the world.

His teaching and research interests are in the field of physicochemical treatment processes (filtration and adsorption based processes), natural treatment systems (bank filtration and soil aquifer treatment), water transport and distribution (water loss management, urban water demand management, corrosion of water pipes) and decentralized water supply systems for small towns and urban poor areas.

http://www.unesco-ihe.org/iu/staffmember/roj

This Course is built up from 5 parts:

1. Introduction

2. Uses, advantages and limitations of RWH system

3. System components and design considerations for roof RWH system

4. Quality aspects of RWH system

5. Examples of RWH systems

Contents

INTRODUCTION INTO RAINWATER HARVESTING

Part 1

Rainwater harvesting (RWH): technology used for collecting

and storing rainwater for human use from rooftops, land

surfaces or rock catchments.

One of the world’s most important ancient water supply

techniques (practiced for more than 4,000 years), is beginning

to enjoy a resurgence in popularity.

Rainwater is an important water source in many areas with

significant rainfall but lacking any kind of conventional,

centralised supply system.

Introduction (1)

Sigiriya, Sri Lanka.

Sigiriya, Sri Lanka. This reservoir cut into the rock was used centuries ago to hold harvested rainwater.

http://www.itdg.org/html/technical_enquiries/docs/rainwater_harvesting.pdf

Cistern of the Maya people, called Chultun Capacity: 45 000 Litres Diameter: 5 m, Catchment area: 150 m²

Source: http://www.irpaa.org.br

Rainwater is also a good option in areas where good quality

fresh surface water or groundwater is lacking.

It could be used as a supplement to piped water supply e.g.

for toilet flushing, washing and garden spraying

RWH is a decentralised, environmentally sound solution,

which can avoid many environmental problems often caused

in centralised conventional large-scale water supply projects.

Introduction (2)

1. Roof catchments• Simple roofwater collection system for households• Larger systems for educational institutions, stadiums, airports, and

other facilities• Roofwater collection systems for high-rise buildings in urbanised

2. Ground catchments (man-made)

3. Rock catchments (natural, impervious outcrops)

4. Collection of storm water in urbanized catchments for

recharge

Types of Rainwater Harvesting Systems

Typical Domestic Rainwater Harvesting System

Source: http://www.eng.warwick.ac.uk/DTU/rainwaterharvesting/index.html

Ground Catchment System

Source: ENSIC (1991)

Ground Catchment System

Rock Catchment System

Source: ENSIC (1991)

USES, ADVANTAGES & LIMITATIONS

Part 2

Use of Harvested Rainwater

Non-potable purposes (mainly in urban areas)- Gardening- Flushing- Washing clothes/cars

Potable purpose after ensuring quality (mainly in rural and peri-urban areas)

Small-scale rainwater harvesting systems and uses

In view of increasing migration to urban area and the emergence of

mega-cities in the next millennium, it is imperative that water supply

systems should be evolved to cater for such a development.

In areas with relatively high rainfall spread throughout the year, where

other water resources are scarce, RWH is an important option, for

example parts of Sri Lanka, Philippines, Indonesia, Nepal and Uganda.

Installation RWH system is mandatory for the construction of buildings

in some towns in India and on the Virgin Islands, USA.

Many government agencies and municipalities worldwide provide

grants/subsidies and technical know-how to promote RWH system.

RWH in Urban Areas

In case of roof catchment systems, there is sufficient

flexibility to utilize systems that will be adaptable to suit all

socio-economic levels of population including the urban poor.

Examples of typical options in urban area

- Rainwater use in households as a supplement

- Public institutions

- High rise building in high density urban areas

- Collection of rainwater in industrial areas

- Use of runoff in airports

- Collection of rainfall from public open spaces for

recharging

RWH in Urban Areas (2)

RWH systems provide water at or near the point where water is needed or used.

Rainwater is relatively clean and the quality is usually acceptable for many purposes with little or even no treatment.

System is independent and therefore suitable for scattered settlements.

Local materials and craftsmanship can be used in construction of rainwater system.

Ease in maintenance by the owner/user

Provides a water supply buffer for use in times of emergency or breakdown of the public water supply systems

Advantages of RWH

Flood control - by greatly reducing urban runoff;

Stormwater drainage - by reducing the size and scale of infrastructure requirements;

Firefighting and disaster relief - by providing independent household reservoirs;

Water conservation - as less water is required from other sources;

Reduced groundwater exploitation and subsidence - as less groundwater is required;

Financial savings – where rainwater can be used in place of water purchased from water vendors.

Advantages of RWH in Urban Areas

The initial cost (mainly of storage tank) may prevent a family from installing a RWH system.

The water availability is limited by the rainfall intensity and available roof area.

Mineral-free rainwater has a flat taste, which may not be liked by many.

The poorer segment of the population may not have a roof suitable for rainwater harvesting.

Domestic RWH will always remain a supplement and not a complete replacement for city-level piped supply or supply from more ‘reliable’ sources.

Limitations of RWH

USES, ADVANTAGES & LIMITATIONS

Part 3

SYSTEM COMPONENTS AND DESIGN CONSIDERATIONS

Part 3

Catchment Area/Roof

- the surface upon which the rain falls

Gutters and Downpipes

- the transport channels from catchment surface to storage

Leaf Screens and Roofwashers

- the systems that remove contaminants and debris

Cisterns or Storage Tanks

- where collected rainwater is stored

Conveying

- the delivery system for the treated rainwater, either by gravity or pump

Water Treatment

- filters and equipment, and additives to settle, filter, and disinfect

RWH System Components

The material of the catchment surfaces must be non-toxic and not contain substances which impair water quality.

Roof surfaces should be smooth, hard and dense since they are easy to clean and are less likely to be damaged and shed materials into water

Precautions are required to prevent the entry of contaminants into the storage tanks.

- No overhanging tree should be left near the roof

- The nesting of the birds on the roof should be prevented

- A first flush bypass such as detachable downpipe should be installed

Design considerations for rooftop catchment systems (1)

All gutter ends should be fitted with a wire mesh screen to keep out leaves, etc.

The storage tank should have a tight-fitting roof that excludes light, a manhole cover and a flushing pipe at the base of the tank.

The design of the tank should allow for thorough scrubbing of the inner walls and floor or tank bottom. A sloped bottom and a provision of a sump and a drain are useful for collection and discharge of settled grit and sediment.

Taps/faucets should be installed at 10 cm above the base of the tank as this allows any derbis entering the tank to settle on the bottom where it remains undisturbed, will not affect the quality of water.

Design considerations for rooftop catchment systems (2)

Rainfall quantity (mm/year)

Rainfall pattern

Collection surface area (m2)

Runoff coefficient of collection (-)

Storage capacity (m3)

Daily consumption rate (litres/capita /day)

Number of users

Alternative water sources

Factors affecting RWH system design

The technical feasibility of roof RWH as a primary source of water is determined by the potential of a rainwater to meet the demand more effectively than other alternatives.

Often the attraction of RWH may be as a supplementary water source to reduce the pressure on a finite primary source or as a backup during the time of drought or breakdown.

The total amount of water that is received in the form of rainfall over an area is called the rainwater endowment of that area.

The collection efficiency accounts for the fact that all the rainwater falling over an area cannot be effectively harvested.

Feasibility of Rainwater Harvesting

The size of supply of rainwater depends on the amount of rainfall (R), the area of the catchment (A) and its runoff coefficient (C).

An estimate of mean annual runoff from a given catchment can be obtained using the equation:

S = R * A * C Where S = Rainwater supply per annum

R = mean annual rainfallA = Area of the catchmentC = Runoff coefficient

The actual amount of rainwater supplied will ultimately depend on the volume of the storage tank or reservoir.

Feasibility of Rainwater Harvesting

The size of roof catchment is the projected area of the roof or the building’s footprint under the

To calculate the catchment area (A), multiply the length (L) and

width (B) of the guttered area. It is not necessary to measure the sloping edge of the roof.

Note that it does not matter whether the roof is flat or peaked. It is the “footprint” of the roof drip line that matters.

Catchment Area Size

Type Runoff coefficient

GI sheets > 0.9 Excellent quality water. Surface is smooth and high temperatures help to sterilise bacteria

Tile (glazed)

0.6 – 0.9 Good quality water from glazed tiles. Unglazed can harbour mould Contamination can exist in tile joins

Asbestos Sheets

0.8 – 0.9 New sheets give good quality water Slightly porous so reduced runoff coefficient and older roofs harbour moulds and even moss

Organic (Thatch)

0.2 Poor quality water (>200 FC/100ml) Little first flush effect; High turbidity due to dissolved organic material which does not settle

Characteristics of Roof Types

Source: http://www.eng.warwick.ac.uk/dtu/rwh/components2.html

Example 1:

For a building with a flat roof of size 10 m x 12 m in a city with the average annual rainfall of 800 mm

Roof Area (A) = 10 x 12 = 120 m2

Average annual rainfall (R) = 800 mm = 0.80 m

Total annual volume of rainfall over the roof

= A * R = 120 m2 x 0.80 m = 96 m3 = 96,000 litres

If 70% of the total rainfall is effectively harvested,

Volume of water harvested = 96,000 x 0.7 = 67,200 litres

Average water availability = 67,200 / 365 ~ 184 litres/ day

There are several options available for the storage of rainwater. A variety of materials and different shapes of the vessels have been used.

In general, there can be two basic types of storage system:

- Underground tank or storage vessel

- Ground tank or storage vessel

The choice of the system will depend on several technical and economic considerations like, space availability, materials and skill available, costs of buying a new tank or construction on site, ground conditions, local traditions for water storage etc.

Storage System

The storage tank is the most expensive part of any RWH system and the most appropriate capacity for any given locality is affected by its cost and amount of water it is able to supply.

In general, larger tanks are required in area with marked wet and dry seasons, while relatively small tanks may suffice in areas where rainfall is relatively evenly spread throughout the year.

Field experiences show that a universal ideal tank design does not exist. Local materials, skills and costs, personal preference and other external factors may favour one design over another.

Storage System

A solid secure cover to keep out insects, dirt and sunshine

A coarse inlet filter to catch leaves etc.

A overflow pipe

A manhole, sump and drain for cleaning

An extraction system that does not contaminate the water e.g. tap/pump

A soakaway to prevent split water forming puddles near the tank.

Additionally features

- sediment trap or other foul flush mechanism

- device to inside water level in the tank

Requirements for Storage System

RWH Brick Jars - Uganda

Source: Rees and Whitehead (2000), DTU, University of Warwick, UK

Rainwater Harvesting - Kenya

Source: John Gould (Waterlines, January 2000)

Ferro-cement jar for rainwater collection - Uganda

Source: DTU, University of Warwick (September 2000)

Underground lime and bricks cistern

Rainwater Harvesting – Sri Lanka

48http://www.greenhouse.gov.au/yourhome/technical/pdf/fs22.pdf

A wooden water tank in Hawaii, USA

Source: Rainwater Harvesting And Utilisation. An Environmentally Sound Approach for Sustainable Urban Water Management: An Introductory Guide for Decision-Makers. ITEC, UNEP, Japan

50http://www.arcsa-usa.org/

52Source: http://www.greenhouse.gov.au

Rainwater Tanks

Storage capacity

When using rainwater, it is important to recognize that the rainfall is not constant through out the year; therefore, planning the storage system with an adequate capacity is required for constant use of rainwater, even during the dry period.

Knowledge of the rainfall quantity and seasonality, the area of the catchment surface and volume of the storage tank, and quantity and period of use required for water supply purposes is critical.

There are two commonly used method to estimate storage requirements.

Storage capacity

Method 1 – Storage required for dry period

A rough estimate of the maximum storage requirement can be made based on the (i) per capita consumption (ii) no of users and (iii) length of the longest dry period

For a household with a 5 people, assuming water use of 20 lpcd and if longest dry period is 30 days and rainwater is the only water source, storage required = 5 x 20 x 30 = 3000 litres

Storage capacity

Method 1 – Storage required for dry period

This simple method assumes sufficient rainfall and catchment area which is adequate, and is therefore only applicable in areas where this is the situation.

It is a method for acquiring rough estimates of tank size.

Storage capacity

Method 2 – Based on rainfall and water demand pattern

A better estimate of storage requirement can be made using the mass curve technique based on rainfall and water demand pattern.

Cumulative rainfall runoff and cumulative water demand in year is calculated and plotted on the same curve.

The sum of the maximum differences, on the either side, between the rainfall curve and water demand curve gives the size of the storage required

Storage capacity

Example 2:

Calculate the size of the storage tank required for a school with 65 students and 5 staff, assuming average water consumption of 5 litres/day.

Roof area = 200 m2.

Assume runoff coefficient of 0.9.

The rainfall pattern in the area is given in the table below

Average daily demand = 70 x 5 = 350 litres

Yearly demand = 350 * 365 = 127750 litres = 127.75 m3 Average monthly demand = 127.75/12 ~ 10.65 m3

Storage capacity calculations

(a) Rainfall pattern - 1

Month Rainfall

mmJan 120Feb 90Mar 70Apr 120May 40June 50July 45Aug 15SepOct 45Nov 70Dec 45

J F M A M J J A S O N D

Calculation of required storage capacity (1)

Required storage capacity = 29.4 m3 say 30 m3

Month Rainfall Rainfall Water Cum. Rainfall Cum. Water Differenceharvested Demand harvested CH Demand CD CH - CD

mm m3 m3 m3 m3 m3

J 120 21.6 10.65 21.6 10.65 10.95F 90 16.2 10.65 37.8 21.3 16.5M 70 12.6 10.65 50.4 31.95 18.45A 120 21.6 10.65 72 42.6 29.4M 40 7.2 10.65 79.2 53.25 25.95J 50 9 10.65 88.2 63.9 24.3J 45 8.1 10.65 96.3 74.55 21.75A 15 2.7 10.65 99 85.2 13.8S 0 10.65 99 95.85 3.15O 45 8.1 10.65 107.1 106.5 0.6N 70 12.6 10.65 119.7 117.15 2.55D 45 8.1 10.65 127.8 127.8 0

Mass curve for calculation of required storage capacity

Cum. Harvested Cum. Demand

Mass curve for calculation of required storage capacity

Harvested Water demand

Storage capacity calculations

(b) Rainfall pattern - 2

Month Rainfall

mmJan 120Feb 100Mar 100Apr 115MayJuneJulyAugSepOct 55Nov 100Dec 120

Months

Calculation of required storage capacity (2)

Required storage capacity = 35.7 + 18.3 = 54 m3

Month Rainfall Rainfall Water Cum. Rainfall Cum. Water Differenceharvested Demand harvested CH Demand CD CH - CD

mm m3 m3 m3 m3 m3

J 120 21.6 10.65 21.6 10.65 10.95F 100 18 10.65 39.6 21.3 18.3M 100 18 10.65 57.6 31.95 25.65A 115 20.7 10.65 78.3 42.6 35.7M 0 10.65 78.3 53.25 25.05J 0 10.65 78.3 63.9 14.4J 0 10.65 78.3 74.55 3.75A 0 10.65 78.3 85.2 -6.9S 0 0 10.65 78.3 95.85 -17.55O 55 9.9 10.65 88.2 106.5 -18.3N 100 18 10.65 106.2 117.15 -10.95D 120 21.6 10.65 127.8 127.8 0

Gutters are channels all around the edge of a sloping roof to collect and transport rainwater to the storage tank.

A carefully designed and constructed gutter system is essential for any roof catchment system to operate effectively.

When the gutters are too small considerable quantities of runoff may be lost due to overflow during storms.

The size of the gutter should be according to the flow during the highest intensity rain. It is advisable to make them 10 to 15 per cent oversize.

Gutters

A general rule of thumb is that 1 cm2 of guttering is required for every m2 of roof area.

Gutters can be semi-circular or rectangular and could be made using a variety of materials:

- Locally available material such as plain galvanised iron sheet (20 to 22 gauge), folded to required shapes.

- Semi-circular gutters of PVC material can be readily prepared by cutting those pipes into two

equal semi-circular channels.

- Bamboo or betel trunks cut vertically in half.

- Wood or plastic

Gutters (2)

Gutters need to be supported so they do not sag or fall off when loaded with water.

The way in which gutters are fixed depends on the construction of the house;

- it is possible to fix iron or timber brackets into the walls, but for houses having wider eaves, some method of attachment to the rafters is necessary.

A properly fitted and maintained gutter-downpipe system is capable of diverting more than 80% of all runoff into the storage tank, the remainder being lost through evaporation, leakage, rain splash and overflow.

Gutters (3)

Gutter configurations

Gutters - Shapes and Configurations

Gutters and Hangers

Shade cloth guttering

Source: Peter Morgan (1998)http://aquamor.tripod.com/RAINWATER.htm

http://www.eng.warwick.ac.uk/DTU/pubs/wp/wp55/8gutter.html

Plastic sheet guttering

Gutter sizingRecommended gutter widths for use in humid tropics

Gutter width (mm) Roof area (m2) served by 1 gutter

100 66

Source: (Still and Thomas, 2002)

Gutter sizingOptimum roof area drainable by square gutters (considering

only conveyance)Square gutters

Slope (%)

0.5 1 2 4

Gutter width

Optimum roof area served by gutter (m2)

33 mm 10 14 20 28

50 mm 29 42 60 85

75 mm 88 125 177 250

100 mm 190 269 380 538

Source: (Still and Thomas, 2002)

Guttering for a 60 m2 roof

Source: http://www.eng.warwick.ac.uk/DTU/rwh

Square 0.5% slope

Square 1% slope

Half round1.0% slope

45o Triangle 1.0% slope

Material use(mm)

214 189 150 175

Gutter width at top (mm)

71 63 96 124

Cross sectional area (cm2)

47 39 36 38

Source: www.sopac.org

Guide to sizing of gutters and downpipes for rainwater harvesting systems in tropical regions

Roof area (m2) served by one gutter

Gutter width (mm)

Minimum diameter of downpipe (mm)

17 60 40

25 70 50

34 80 50

46 90 63

66 100 63

128 125 75

208 150 90

First flush system (1)

Debris, dirt, dust and droppings will collect on the roof of a building or other collection area.

When the first rains arrive, this unwanted matter will be washed into the tank. This will cause contamination of the water and the quality will be deteriorated.

Many RWH systems therefore incorporate a system for diverting this ‘first flush’ or ‘foul flush” water so that it does not enter the storage tank.

Several first flush system are in use. The simplest one is a manually operated arrangement whereby the inlet pipe is moved away from the tank inlet and then replaced again once the initial first flush has been diverted.

For an average roof catchment it is suggested that the first 20–25 L could be diverted or discarded.

First flush devices should be regarded as an additional barrier to reduce contamination and should not be used to replace normal maintenance activities designed to keep roof catchments reasonably clean.

The inlet pipe to all rainwater tanks should be easily detachable so that, when necessary, the tank can be bypassed. Manual detachment could be used as an alternative to an engineered first flush device, although the level of control will not be as good.

Developed by Khon Kaen University, Thailand

Device for separating rainwater from roof-accumulated impurities

Roof catchment system with filter and storage tank

Storage tank & first flush - Malaysia

QUALITY ASPECTS OF RWHPart 4

The quality of rainwater is relatively good but it is not free from all impurities.

Analysis of stored rainwater has shown some bacteriological contamination.

The rainwater is essentially lacking in minerals, the presence of which is considered essential in appropriate proportions.

Cleanliness of roof and storage tank is critical in maintaining good quality of rainwater.

The storage tank requires cleaning and disinfection when the tank is empty or at least once in a year.

Quality of Rainwater (1)

The extraction system (e.g. taps/faucets, pumps) must not contaminate the stored water.

The first run off from the roof should be discarded to prevent entry of impurities from the roof.

Some devices and good practices have been suggested to store or divert the first foul flush away from the storage tank.

In case of difficulties in the rejection of first flow, cleaning of the roof and gutter at the beginning of the rainy season and their regular maintenance are very important to ensure better quality of rainwater.

Quality of Rainwater (2)

Dust from the soil, and droppings of birds and animals could be the source of contamination by the bacteria.

When first flush eliminating devices are absent, all the indicator bacteria are generally present in water samples in numbers beyond what is acceptable by any standards.

Tree hanging in the vicinity, definitely enhances the possibility of contamination due to increased access of the roof to birds and animals. Also leaves contribute to organic loading of the water samples, which in turn act as nutrient for bacterial growth.

Quality of Rainwater - Bacteriological

• Rainwater is generally of very good chemical quality. However, it may not meet WHO drinking water quality standards, specifically microbiological quality standards, hence some disinfection is recommended.

• Rainwater can be used for drinking, if it is clear, has no or very little taste or smell and is from well maintained system.

• Disinfection can be done by:

• boiling the water in before consumption

• adding chlorine compounds/bleaching powder in required quantity to the water stored in the tank

• using slow sand filtration

• solar disinfection (SODIS)

Disinfecting rainwater

For disinfection using bleaching powder, the general dosage recommended is 10 mg of bleaching powder containing 25% of free chlorine per litre of water. This meets the required standard of 2.5 mg of chlorine per litre of water.

After adding the bleaching powder, the water should be stirred thoroughly for even distribution of the disinfectant agent. The water should be kept without use for about 30 minutes after adding bleaching powder.

Disinfecting rainwater (2)

The simple operation and maintenance of RWH systems is one of the most attractive aspects of the technology.

The extent of maintenance required by a basic privately owned household RWH system includes

- Regular cleaning of the roof tops and gutters

- Frequent cleaning of storage tanks

- Inspection of gutters and feeder pipes and valve chambers to detect and repair leaks

When ground catchment is used for collection and/or ground tank is used for storage, proper fencing of both is recommended to keep the children and animals away, thus avoiding contamination and risks of falling into the tank.

Operation and maintenance

One example of a flat screen over the gutter to keep large debris out of the tank.

A problem with gutter screens is that they require a lot of maintenance to keep leaves and debris from piling up and blocking the screens.

Also, dirt on the leaves can still be washed into the storage tank.

Source: Guidelines on Rainwater Catchment Systems for Hawaii

95Source: http://www.rainharvesting.com.au

Leaf Eater®/Leaf Beater®/Leaf Catcha®

Tank desludging and cleaning (1)

Accumulated sediments can be a source of chemical contamination and off-tastes and odours. All tanks should be examined for accumulation of sediments every 2–3 years.

Sludge can be removed by siphoning without emptying the tank. Sludge may also be pumped from the tank with

minimum loss of water by using a suitable motor-operated pump and attachments.

Sludge can also be removed by draining and cleaning the tank. If a drain plug is provided at the base of the tank, water can be run to waste to discharge the sludge. Once the tank is empty, the remaining sludge can be scooped up and removed through the access opening.

Tank desludging and cleaning (2)

It is important to check the structural condition of the tank before choosing a method of cleaning.

Cleaning should generally be limited to removing accumulated sediments, leaf litter etc. Harsh (chemical) cleaning methods may accelerate deterioration, for example, removing the protective layer on the inside walls of a steel tank will lead to tank corrosion.

After cleaning, it is recommended that the internal walls and floor of the tank be rinsed with clean water. Rinse water and sediment should be run to waste.

Where cleaning necessitates entering the tank, take care to ensure adequate ventilation is provided and an additional person is in attendance.

· Nationwide rainwater harvesting programme which dramatically improved the rural water supply coverage, especially in North eastern Thailand

• 10 million rainwater jars constructed in 5 years (1985-1990).

· Factors favouring rapid development RWH programme

• a real felt need for water

• a preference for the taste of rainwater

• the availability of cheap cement and skilled artisans

• a pool of indigenous engineers, technicians and administrators committed to rural development programme

The Thai Rainwater Jar Programme

Thai JarKhon Kaen, Thailand

Source: http://www.ircsa.org

Rainwater Harvesting - Australia

More than one million people in Australia rely on rainwater as their primary source of water supply

Rainwater Harvesting - Australia

In Australia the use of domestic rainwater tanks is an established and relatively common practice, particularly in rural and remote areas.

Between 1994 and 2001, 16% of Australian households used rainwater tanks, with 13% of households using tanks as their main source of drinking water.

7% of the capital city households and 34% of non-capital city households have rainwater tanks.

In a 1996 South Australian survey, 28% of Adelaide households used rainwater tanks as the primary source of drinking water compared to 82% households in the rest of the State.

Source: Guidance on use of rainwater tank. En Health, Australian Government 2004

Rainwater harvesting system, in Patan, Nepal

1 - Overhead tank2 - Downtake PVC pipe from roof 3 - First phase storage drum4 - Overflow goes into underwater tank5 - Pump to lift water to overhead tank6 - Sediment discharge tap7 - 50,000 litre underground ferrocement tank

Source: Nepali Times (16-22 August 2002)

Rainwater Harvesting in Tokyo

Rainwater Harvesting from Domed Stadium in Japan

Source: Zaizen et al. (1999)

Rainwater Harvesting from Domed Stadium in Japan

_________________________________________________________Stadium Tokyo Fukuoka Nagoya_________________________________________________________Catchment area for storage (m2) 16,000 25,900 35,000

Capacity of detention tank (m3) 1000 1800 1500

Utilization Flush toilets Flush toilets, Flush toiletswatering plants watering plants

__________________________________________________________

Source: Zaizen et al. (1999)

Rainwater Harvesting at Changi Airport - Singapore

Rainfall from the runways and the surrounding green areas is diverted to two impounding reservoirs.

One of the reservoirs is designed to balance the flows during the coincident high runoffs and incoming tides, and the other reservoir is used to collect the runoff.

The water is used primarily for non-potable functions such as fire-fighting drills and toilet flushing.

Such collected and treated water accounts for 28 to 33% of the total water used, resulting in savings of approximately S$ 390,000 per annum.

Rainwater Harvesting in Presidential Estate, New Delhi, India

- About 7000 residing in the estate and about 3000 visitors

every day. There is also famous “The Mughal Garden”.

- Total water demand 2 million litres per day

- 30% of demand met by Groundwater wells in the estate and

groundwater level is going down rapidly)

Rainwater Harvesting in Presidential Estate, New Delhi, India

Rainwater from the northern side of the roof and paved areas surrounding the presidential palace is diverted to an underground storage tank of 100,000 litres capacity for low quality use (5%).

Overflow the rainwater storage tank is diverted to two dug wells for recharging.

Rainwater from southern side of the roof is diverted for recharging a dry open well. Rainfall runoff from the staff residential area is also diverted to dry wells.

15 m deep recharge shafts have been constructed for recharging.

Water Supply Plant, installed at the UK's Millennium Dome can supply around 500 m3 per day of reclaimed water to flush all of the toilets and urinals on the site.

Water is reclaimed from greywater produced by the hand wash basins, rainwater from the dome's roof, and groundwater from the chalk aquifer which is located below the site.

Water Supply at Millennium Dome, London

Rainwater is collected from dome roof and adjacent areas (100,000 m2)

Size of collection tank is 800 m3

Reed beds are used for treatment

Water Supply at Millennium Dome, London

The success of any rain water harvesting system or programme ultimately depends on the interest, enthusiasm and active support of the user community for the technology.

RWH system, even if technically appropriate and justified based water resources condition, it is not likely to be successful if it is socially unacceptable or inappropriate in anyway.

Local customs, perceptions and preferences must be given high priority when considering the feasibility of the technology and possible implementation strategies.

Socio-cultural Considerations (1)

It is always vital to be sensitive to local perceptions regarding quality and suitability of rainwater.

Although some people regard rainwater as sweet and tasty (especially those used to drinking somewhat saline groundwater), others consider it to be flat and tasteless (particularly when compared to water with high mineral content).

Local customs, perceptions and preferences must be given high priority when considering the feasibility of the technology and possible implementation strategies.

Socio-cultural Considerations (2)

Public awareness and education are essential in order to improve acceptance of rainwater collection and

utilisation.

Efforts should be made to change public perception of rainwater from being viewed as a nuisance to being

viewed as an asset.

Demonstration projects are key for improving public acceptance and assisting in the removal of institutional barriers.

To promote rainwater utilisation, basic policies, implementation strategies, technology development and networking are required.

Public Awareness and Demonstration

Rainwater Harvesting and Utilization. An Environmentally Sound Approach for Sustainable Urban Water Management: An Introductory Guide for Decision-Makers. IETC-UNEP, Japan.

Rainwater catchment systems for Household Water Supply (1991). Environmental Sanitation Reviews No No 32. ENSIC, Bangkok, Thailand.

UNEP-IETC (1999) Proceedings of the International Symposium on Efficient Water Use in Urban Areas - Innovative Ways of Finding Water for Cities. (8 to 10 June 1999), Kobe, Japan.

Gould, J. and Nissen-Petersen, E. (1999) Rainwater Catchment Systems for Domestic Supply. IT Publications, London

Hasse, R. (1989) Rainwater Reservoirs- Above Ground Structures for Roof Catchment. GTZ.

NGO Forum and SDC (2001) Rain Water Harvesting System. NGO Forum for Drinking Water Supply and Sanitation and SDC,

Bangladesh.

Bibliography

International Rainwater Catchment Systems Association http://www.eng.warwick.ac.uk/ircsa/

American Rainwater Catchment Association

http://www.arcsa-usa.org/

Centre for Science and Environment (CSE), India

http://www.rainwaterharvesting.org

Development Technology Unit, School of Engineering, University of Warwick, UK

http://www.eng.warwick.ac.uk/DTU/rwh/index.html

Chennai Metrowater, India http://www.chennaimetrowater.com/rainwaterfaqs.htm

Rainwater Partnership

http://www.rainwaterpartnership.org/

Web Resources on RWH

Lanka Rainwater Harvesting Forum

http://www.rainwaterharvesting.com

Intenational Rainwater Harvesting Alliance

http://www.irha-h2o.org/

Greater Horn of Africa Rainwater Partnership (GHARP)

http://www.gharainwater.org/

The Web of Rain

http://www.gdrc.org/uem/water/rainwater/rain-web.html

Web Resources on RWH (2)

rainwater harvesting course 6 1 teacher saroj sharma s.sharma@unesco-ihe.org

water transport

various water supply

rural water supply projects

important water source

corrosion of water pipes

centralised supply system

urban water demand management

roof rwh system

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