Conceptual framework for rainwater harvesting in an urban...

CAPTAÇÃO E MANEJO DE ÁGUA DE CHUVA PARA

SUSTENTABILIDADE DE ÁREAS RURAIS E URBANAS – TECNOLOGIAS E CONSTRUÇÃO DA CIDADANIA

TERESINA, PI, DE 11 A 14 DE JULHO DE 2005

Conceptual framework for rainwater harvesting in an urban context

The example of Bangalore, IndiaS.Vishwanath

www.rainwaterclub.org

Introduction: The sustainable and equitable supply of water to urban cities in growing

economies like India is a matter receiving serious attention of policy makers and governments

ever since the International Decade on water supply and sanitation. Subsequently the setting

of the Millennium Development Goals by the UN has acted as a spur for further improving

the process. The case study here seeks to describe how such a process factors in rainwater

harvesting as a component of the overall water supply and management plan of the city of

Bangalore in South India and the capital city of the state of Karnataka.

The setting: Bangalore is located at an altitude of 921 metres above sea level with no

perennial river flowing within 100 kilo-metres of it. The current population of the city is

estimated as close to 6 million. With its reputation as the ‘silicon valley’ of India it has also a

booming economy especially that of the software and IT sector attracting capital and people

from the world across. Provision of water to this burgeoning population is a challenge to the

government and the water supply provider –the Bangalore Water Supply and Sewerage

Board.

5º Simpósio Brasileiro de Captação e Manejo de Água de Chuva, Teresina, PI, 11-14/07/2005

The history: Till 1896 the city depended on its lakes for water supply. Due both to a shortage

of water and the pollution of the lakes the first major water supply scheme was drawn up for

the city. A reservoir was built across the river Arkavathy at a place called Hessarghatta and

water was pumped in to the city from a distance of 20 kilometers. In 1936 this water proved

inadequate and another reservoir was built across the same river but downstream. Water was

now pumped in from a distance of 40 kilometers. By 1974 the city required more water and

therefore a scheme was taken up to pump water from the river Cauvery a perennial river. This

water had to be pumped a distance of 95 kilometers and 500 metres high. It is estimated that

74 MW of power is required daily to pump this water into the city.


Year Water source Distance Scheme Design capacity Remarks Km. name MLD

1896 1933

Hessarghatta reservoir Thippagondanahalli reservoir

20 40

ChamarajsagarT.G.Halli Sub-total

36 148 184

River source & lake dry River source & lake dry No longer reliable

1974 Cauvery I stage 95 T.K.Halli 135

1982 Cauvery II stage 95 T.K.Halli 135

1993 Cauvery III stage 95 T.K.Halli 270

2003 Cauvery IV stage Phase I

95 T.K.Halli 270

Sub Total 810 Currently being supplied

2007 Cauvery IV stage 95 T.K.Halli 500 Proposed project Phase II

Total 1310

Grand total 1494

HISTORY AND ECOLOGICAL FOOTPRINT OF WATER TO BANGALORE

Limits to water availability: With the total quantum of 1494 million litres per capita

per day the city will have reached its quota of allocation from the river Cauvery where it

draws it water as the most reliable source. Current standards of water requirement as laid

down in the State water policy prescribe a 200 litres per capita per day. With reliable sources

of supply being only 1310 million litres per day, this amount of water will be sufficient for a

population of 6.55 million, a figure which will be reached in the near future.

Solutions for sustainability: It is clear that economic and urbanization forces will place

higher and higher demand on scarce water resource availability. Therefore the city sees the

following approaches for ensuring water in the future in adequate quantities for the cities

requirement


- Demand management and reduction of demand - Reuse of water for lower level purposes - Recycling of water at various scales - Rainwater harvesting to supplement water requirements

This paper will focus on the last item i.e. rainwater harvesting and its role in sustainable

water supply in an urban context

RAINWATER HARVESTING: It is defined as the process of collection and storage of

rainwater for future productive use. The artificial recharge of groundwater is also seen Interest

has been sparked in a re-look at this traditional system due to a sustained systematic campaign

lead by NGO’s like the Centre for Science and Environment –CSE-www.cseindia.org and

other groups. The Ministry of Environment of the State Government of Karnataka sponsored

a study called ‘The Conceptual Frame for Rainwater harvesting in Bangalore’. The study was

carried out by a private consultancy firm STEM (Centre for Symbiosis of Technology,

Environment and Management) in the year 2001 and the report submitted to the Government

of Karnataka.

National water policy and rainwater harvesting: Rainwater harvesting is gradually being

accepted in the National mainstream of water resource planning and management. The

National Water Policy-April 2002 for example, states in item 3.2 that ‘Non-conventional

methods for utilization of water such as through inter-basin transfers, artificial recharge of

ground water and desalination of brackish or sea water as well as traditional water

conservation practices like rainwater harvesting, including roof-top rainwater

harvesting, need to be practiced to further increase the utilizable water resources. Promotion

of frontier research and development, in a focused manner, for these techniques is necessary.

Further it is made clear that in so far as drinking water facilities are concerned ‘ Adequate safe

drinking water facilities should be provided to the entire population both in urban and in rural

areas. Irrigation and multipurpose projects should invariably include a drinking water

component, wherever there is no alternative source of drinking water. Drinking water needs of

human beings and animals should be the first charge on any available water.’ Since the aim of

rooftop rainwater harvesting especially in rural areas is to provide drinking water for both

humans and animals the National water policy supports these initiatives State Water Policy

and rainwater harvesting: In India water is a state subject. The state, or province as it is

called in many countries, has full jurisdiction and authority in matters of water supply


provision and can evolve and implement policies on their own .The Karnataka State Water

Policy is even more clear It wants to ‘ Provide drinking water at the rate of 55 litres per

person per day in the rural areas, 70 litres per person per day in towns and 100 litres per

person per day in the city municipal council areas and 135 litres per person per day in city

corporation areas.’ Specifically on rainwater harvesting the Policy states ‘The efficiency of

utilization of water will be improved and awareness about water as a scarce resource

fostered.’ The Action agenda states that ‘Rainwater harvesting and water conservation will be

encouraged. Conservation consciousness will be promoted through education, regulation

incentives and disincentives. Formulate and implement projects and schemes of rainwater

harvesting and recharging of underground water sources, with community participation.

While the State policy does not explicitly talk about rooftop rainwater harvesting the message

is clear that it will be encouraged through a system of education, awareness, training and

project support. Water requirement in a city: Typically water requirement in a city can be

classified into

-domestic consumption requirement for houses, flats, apartments

-commercial requirement for hotels, restaurants, hospitals, schools

-industrial requirements for process use

-landscape requirements for parks, playgrounds, water sports

-environmental requirements for micro-climate balancing

-ecological requirements for maintaining and enhancing bio-diversity

In all cases rainwater has a role to play in satisfying the demand.

CONCEPTUAL FRAMEWORK: The conceptual framework sought to work along these lines a) Determine the total volume and

reliability of rainfall in the city and estimate rainwater endowment

b) Determine the forms of harvesting it and storing it. c) Understand the capture and use potential of surface water,

shallow ground water and deep groundwater. d) Determine the flows from various catchment surfaces such as rooftops,


paved area, unpaved area, roads e) Determine the best methods and techniques of harvesting rainwater and optimize storage systems f) Understand the roles of various stake holders in the process and their contribution towards rainwater harvesting

g) Determine the cost economics of rainwater harvesting h) Determine the Information Education Communication –IEC-campaign, the training

requirements, the legal framework and the economic incentives necessary to make rainwater harvesting possible in the city.

RAINFALL ANALYSIS FOR BANGALORE CITY: The 4 rainfall measuring

stations with an average of 26 years record were studied. The annual average rainfall was

seen to be Bangalore city 928 mm Bangalore Airport

795 mm 14 km. from the city center to the East

Hebbal 797 mm 12 km. from the city center to the North

Kengeri 900 mm 10 km. from the city centre to the South-West

Weighted average

846 mm

SURFACE WATER FLOWS AND STORAGE: Being located on a ridge, all water flows

away from the city of Bangalore and no water flows in. Three major valleys drain storm water

out of the city. The city was dotted with man made lakes called ‘tanks’ in the past. A

traditional way of storing rainwater for agricultural use by constructing an earthen

embankment across a drainage valley. The city had 262 such ‘tanks’ in the year 1960. Due to

urbanization and the filling up of these ‘tanks’ and their conversion to other land-uses many

of them have disappeared. The latest figure indicates the presence of about 82 ‘tanks’ only.

GROUNDWATER: Bangalore city had close to 30,000 open wells which supplied water for

almost all purpose. Due to many reasons these wells have been abandoned or filled up

including the fact that many dried up, were contaminated with sewage, land values shot up

and the conversion of wells to built up land became more profitable etc. Groundwater occurs

in the weathered mantle of granites, granite gneiss and schistose belts. The rocks are highly

weathered in the entire geographical area giving rise to many cleavages, joints, cracks and


crevices of the weathered rock. In the 1960’s and 1970’s groundwater was used

predominantly by means of open wells. The depths of these wells ranged from 2 to 15metres.

The wells had good yield of between 8 to 10 cubic metre per hour and a recuperation time of

6 to 8 hours. There has been a gradual shift to deep bore wells now and especially in the

periphery of the city bore wells have been drilled to depths of 400 metres. It is estimated that

there are over 100,000 bore wells in Bangalore city alone. Bangalore is thus faced with the

classic paradigm as described by Brian Morris of the British Geological Survey and as

indicated in the UNEP website. Ground water tables in the city centre serviced by the water

supply provider are actually rising due primarily to heavy leakages of the order of 37% from

the distribution system – nearly 300 million litres per day leaks into the ground according to

one calculation, the non-abstraction of well water by people serviced by subsidized piped

water, the leakage from inadequate sewage collection system and the large abandonment of

wells


Source Brian Morris- British geological Survey 2001

RAINWATER INCIDENT ON THE CITY: The city of Bangalore has a land use area for

which a Comprehensive Development Plan exists of 1279 square kilometers. The rainwater

incident on the city on various land use are as below

Land use Square kilo-metres Equivalent Million litres per day

Residential 243.69 565

Commercial 16.44 38

Industrial 38.44 89

Public and semi public 77.88 181


Parks and open spaces 49.09 114

Transportation 116.97 271

Unclassified 22.14 51

Spotted development 32.35 75

Sub –total 597.00 1383 (Development Area)

Green belt 682.00 1581

1279.0 2964

These figures have been a revelation. For example even considering the metropolitan

area of 597 square kilometers the incident rainfall is the equivalent of 1383 million litres

per day , more than 1310 million litres per day, the total water that will be pumped in to

the city reliably after the completion of all piped water schemes proposed. Adding the

additional rainwater falling in the green belt which is of the order of 1581 million litres

per day planning for rainwater harvesting would make ecological and economic sense.

Expert opinion has projected three scenarios with regard to rainwater harvesting

AREA Rainwater Incident Volume harvestable with collection

ratio MLD 20% 10% 5%


MLD

Development 1383 277 138 69

Green belt 1581 316 158 79

Total 2964 593 296 148

POLICY RECOMMENDATIONS FOR RAINWATER HARVESTING: 1 Launch an IEC –Information, education and communication – campaign. 2 Create demonstration effect through model projects 3 Take legal measures to introduce rainwater harvesting for buildings and industries compulsorily 4 Create Incentives through economic measures such as subsidies, loans or reduced water bills 5 Train architects, engineers and plumbers 6 Budget for rainwater harvesting mandatorily in all departments 7 Revive traditional structures of rainwater harvesting such as lakes, tanks and temple ponds

ACHIEVEMENTS:

1. The building bye laws have been modified and rainwater harvesting is now mandatory for

all new buildings in the city. The buildings of plinth area 100 square metre and above or on

plots larger than 200 square metres have to adopt rooftop rainwater harvesting.

Building bye-laws: Bangalore was the first city in Karnataka state to incorporate rainwater

harvesting into its bye-laws. The Bangalore Mahanagara Palike (the City Corporation)

building bye-laws as applicable from 6th

June 2004 incorporate rainwater harvesting as a mandatory component of any

new building sanction. The relevant article in the bye-law reads:

32.0 RAIN WATER HARVESTING. � (a) Every building with a plinth area of exceeding 100 sq mtrs and built on a site measuring not less than 200 sq mtrs shall have one or more Rain Water Harvesting structures having a minimum total capacity as detailed in Schedule XII. Provided that the Authority may approve the Rain Water Harvesting structures of specifications different from those in Schedules – XII, subject to the minimum capacity of Rain Water Harvesting being ensured in each case. � (b) The owner of every building mentioned in the bye-law 32 (a) shall ensure that the Rain Water Harvesting structure is maintained in good repair for storage of water for non potable purposes or recharge of groundwater at all times. � (c) The Authority may impose a levy of not exceeding Rs. 1000/- per annum for every 100 sq. mtr of built up area for the failure of the owner of any building mentioned in the bye-


law 32(a) to provide or to maintain Rain Water Harvesting structures as required under these byelaws.

SCHEDULE XII (Bye-law 32) RAIN WATER HARVESTING

Rain water harvesting in a building site includes storage or recharging into ground of rain

water falling on the terrace or on any paved or unpaved surface within the building site. 1 The

following systems may be adopted for harvesting the rain water drawn from terrace and the

paved surface. i) Open well of a minimum of 1.00 metre diameter and 6 metre in depth into

which rain water may be channeled and allowed after filtration for removing silt and floating

material. The well shall be provided with ventilating covers. The water from the open well

may be used for non potable domestic purposes such as washing, flushing and for watering

the garden etc. ii) Rain water harvesting for recharge of ground water may be done through a

bore-well around which a pit of one metre width may be excavated up-to a depth of at least

3.00 metres and refilled with stone aggregate and sand. The filtered rain water may be

channeled to the refilled pit for recharging the bore-well. iii) An impervious storage tank of

required capacity may be constructed in the setback or other than space and the rain water

may be channeled to the storage tank. The storage tank may be raised to a convenient height

above the surface and shall always be provided with ventilating the surface and shall always

be provided with ventilating covers and shall have draw-off taps suitably placed so that the

rain water may be drawn off for domestic, washing, gardening and such other purposes. The

storage tanks shall be provided with an overflow. iv) The surplus rain water after storage may

be recharged into ground through percolation pits or trenches or combination of pits and

trenches. Depending on the geomorphologic and topographical condition, the pits may be of

the size of 1.20 m width x 1.20 m length x 2.00 m to 2.50 metre depth. The trenches can be or

0.60 m. width x 2.00 to 6.00 metre length x 1.50 to 2.00 mtr depth. Terrace water shall be

channeled to pits or trenches. Such pits or trenches shall be backfilled with filter media

comprising the following materials. a) 40 mm stone aggregate as bottom layer upto 50% of

the depth; b) 20 mm stone aggregate as lower middle layer upto 20% of the depth; c) Coarse

sand as upper middle layer upto 20% of the depth; d) A thin layer of fine sand as top layer; e)

Top 10% of the pits/trenches will be empty and a splash is to be provided in this portion in

such a way that roof top water falls on the splash pad. f) Brick masonry wall is to be

constructed on the exposed surface of pits/trenches and the cement mortar plastered. The

depth of wall below ground shall be such that the wall prevents lose soil entering into

pits/trenches. The projection of the wall above ground shall atleast be 15 cms; g) Perforated


concrete slabs shall be provided on the pits/trenches. v) If the open space surrounding the

building is not paved, the top layer up-to a sufficient depth shall be removed and refilled with

course sand to allow percolation of rain water into ground. 2 The terrace shall be connected to

the open well/borewell/storage tank/recharge pit/trench by means of H.D.P.E./P.V.C. pipes

through filter media. A valve system shall be provided to enable the first washings from roof

or terrace catchment, as they would contain undesirable dirt. The mouths of all pipes and

opening shall be covered with mosquito (insect) proof wire net. For the efficient discharge of

rain water, there shall be at least two rain water pipes of 100 mm dia mtr for a roof area of

100 sq mtrs. 3 Rain water harvesting structures shall be sited as not to endanger the stability

of building or earthwork. The structures shall be designed such that no dampness is caused in

any part of the walls or foundation of the building or those of an adjacent building.

The byelaw is quite clear in stating the techniques of rooftop rainwater harvesting. At worst it

can be said that it is too clear and too specific and seems too focused without lee way for new

ideas and developments in the sector.

1 A series of IEC activities have occurred. For example 18 workshops were conducted by an organization called the Environmental Management Policy Research Institute for professionals and lay persons on rooftop and other forms of rainwater harvesting. Over 1000 people attended the half day workshops. Training programmes were also carried out by associations like the Institute of Architects, the Institute of Engineers and others. 2 Model projects have been taken up starting from the Governor’s residence which harvests water from it entire 7 Hectare campus. Government buildings like the General Post Office, Hospitals etc have rainwater harvesting structures. 3 The Rain Centre called Resource Aqua International network -R.A.I.N – has conducted a series of workshops for plumbers. 4 Over 50 schools have taken water literacy programmes for over 1000 school children. 5 A Lake Development Authority has been constituted with a specific mandate of preserving the city’s water bodies and restoring them ecologically. The Lake Development Authority has restored 14 lakes at the last count and is drawing up plans for the preservation and restoration of all other water bodies in the city. 6 Over 5000 individual homes now have rainwater harvesting facilities. It is estimated that 500 million litres of water per year is being harvested in these homes 7 Over 500 apartments have rainwater harvesting facilities. It is estimated that around 400 million litres of water per year is being harvested here. 8 Over 300 industries are harvesting water. It is estimated that 2100 million litres per year is being harvested here. 9 Over 15 parks harvest rainwater. It is estimated that 74 million litres of water is being harvested annually in the parks.


FAILURES OR NON-PROGRESS: 1 Economic incentives have yet to come in for rainwater harvesting. 2 A Resource centre by the government to advise citizens on the best and most appropriate method to harvest rainwater is yet to be set up. 3 There is persistent problems in institutional coordination to bring a holistic method of rainwater harvesting 4 There is still no scientific data on the best method for rainwater recharge. Codes of procedure for design are yet to be worked upon, which will enable engineers, architects, builders and hydro-geologists to incorporate correct designs in their projects 5 Catchment management strategies are yet to be evolved for the lakes and

tanks of Bangalore. Sewage inflow into the lakes is a regular problem.

Some examples are described in detail in the following pages

A Rainwater harvesting system

Introduction: Rainwater harvesting is the process of collecting, storing and usingrainwater for a productive purpose. One simple way for people to start harvesting rainwater is by building a RAINBARREL SYSTEM. A Rain barrel is a simple rainwater storage drum shown in picture below. It isplaced on a platform 18 inches high. It has a tap to enable drawal of water from a bucket or a hosepipe. The rain barrel comes along with a first rain separator and a filter to improve the quality of the rain water collected. The filter is a small-perforated aluminum basket with two layers of sponge on it.

Rain barrel on a platform and top basket/sponge Filter

How much rainwater can a Rain Barrel collect? If the Rain Barrel is used up and emptied every time it fills up, it can collect a lot ofrainwater. In Bangalore for example, a 500 litre Rain Barrel collecting rainwater from


a 50 square meter roof area can collect nearly 23,000 litres of water in a year. Similarly a1000 litre Rain Barrel can collect nearly 35,000 litres of water in a year. Space and cost. The space required for a Rain Barrel is 3’6” x 4’. Given average considerationinstalling a Rain Barrel should cost about Rs 2700/-. For a 1000 litre Rain Barrel thecost should be Rs 4300/-. What else can we do with the Rain Barrel? Every Rain Barrel has a tap and an overflow outlet. The water collected in the RainBarrel can be used to recharge open wells or bore wells. Using a hosepipe and aZero-B type filter the tap can be connected to the bore well or sump tank. Overflows from Rain Barrels can also be used for recharging the ground.

What are the benefits of a Rain Barrel? Rainwater harvesting through the Rain Barrel generates water for productive usewhich otherwise would have been wasted. It also helps mitigate urban flooding andreduces pressure on city level water supplies and groundwater extraction.

Installing RAIN BARRELS is the easiest and cheapest way to participate in therainwater harvesting movement and make a positive difference to society.

Bangalore:

No. of

rainy days

Year RAIN (mm)

Annual RAINFALL

on 50sq m roof

area

Volume of

rainwater collected in a 500

litre Rain barrel

Overflow from the

rain barrel

for recharge

Volume of

rainfall collected

in a 1000

litre Rain barrel

Overflow from the

1000 litre

barrel for

recharge

62 1994 695 34765 21395 13370 27480 7285 54 1995 619 30935 18820 12115 26455 4480 66 1996 849 42465 24515 19215 31840 10625 57 1997 1155 57740 21355 36385 29855 27885 62 1998 1135 57515 23425 34090 37150 20365 62 1999 1088 54405 23540 30865 34875 19530 68 2000 1189 59445 24445 35000 35665 23780 62 2001 985 49280 23460 25870 35790 13540


RAINWATER HARVESTING FOR PARKS

The garden city: Bangalore city and citizens are quite proud of their parks. In the recent years, thanks to the efforts of the Bangalore Mahanagara Palike and the Horticulture Department of the Government of Karnataka, parks have seen a magnificent revival. Attracting the old for their brisk morning and evening walks and the young just to sit and be with nature, parks have truly become the socializing centre for communities. With a tradition for raising excellent nurseries and plants the green thumbed gardeners of Bangalore deserve applause for their beautiful work.

A green island in a concrete jungle

Water: There is however a small cause for concern. Parks demand water right through the


year and especially in summer. 2 litres of water per square metre is the norm used to calculate water demand. Many parks however do not have adequate water to meet this demand. Though some do get water from the BWSSB and some from their own bore-well it has to be brought in tankers for many. One possible solution being discussed is to harvest rainwater to at least meet partially the water requirement of the park. How is this to be done? An example is presented below.

Water requirements for parks are high

This park in question has a 2500 square metre area measuring roughly 50 metres x 50 metres. The landscaped or planted area is about 2000 square metres. The water demand is therefore about 4,000 litres per day. In a year the water requirement is about 1200 kilo-litres considering water requirement for 300 non-rainy days.

Rainwater harvesting: Rainwater harvesting is simply the process of collecting and storing water for later productive use. There are two basic ways of rain harvesting, storage of rainwater or its recharge into the ground. Storage may be a limited option in open ponds because of the large evaporation losses and the possibility of mosquito breeding in open water bodies. With an average rainfall of 970 mm, rainwater falling on the park in a year is about 2425 kilolitres of which about 50 % can be harvested. This means 1212 kilolitres or about 100% of the yearly requirement for watering the park can be met through rainwater harvesting. Harvested rainwater is definitely not a replacement for other sources of water but a supplement.


The well diggers and the wells they dig

The harvesting in this particular case was done through four recharge and withdrawal wells based on the infiltration capacity during a heavy downpour of 50 mm per hour. For each quadrant of the park a 3 feet diameter and 22 feet deep well was dug and lined with concrete rings. Water was struck at 12 feet depth in the month of January and the well was continued further by about 10 feet. The well will be observed for its behavior in the summer months and if need be deepened. Rainwater from a quadrant of about 25 x 25 metre will be led into this well through swales and a silt trap in the rains to recharge and replenish the aquifer. The well water will be drawn in the non-rainy days through a portable ½ H.P pump with a mist sprayer for watering. It is expected that open well water will be sufficient for the park right through the year. Surprising as it may sound in many places in the city water tables are actually rising. This is thanks to the BWSSB which gives piped water to each house and therefore there is no withdrawal from wells. It also helps that 37% of this piped water leaks and recharges the groundwater. Further augmentation comes from sewage but that is not so welcome. Well diggers out of a job for some time are back in business this time digging recharge wells for rainwater harvesting.

Sustainability: Parks will become sustainable for their water requirement only if the landscaping changes to less water intensive ones. Further requirements would be the installation of drip irrigation systems and a switch from water intensive grass based parks to more a shrub, bush and tree based model with xeri-scaping. Efficient ways to water plants without water wastage and evaporation losses will need to be found. Rainwater harvesting and the use of open well water wherever hydro-geologically possible will be the key to water sustainability of our parks so that they remain beautiful forever.

Rainwater harvesting in slums

Rooftop rainwater harvesting is the process of collecting and storing rain for productive use. Since the last decade the technique has seen a rediscovery and is gaining prominence. At the last count 100 countries had resorted to this system in some form or the other.


The benefits of rainwater harvesting are many. It provides additional water for a families requirement, reduces water bills, it prevents flooding and water stagnation and it can increase groundwater levels where it is used for recharge.

Slums and rainwater harvesting:

While large clean roofs are ideal for collecting rainwater from the rooftops, slum houses can also benefit from this technique. In a recent initiative, an NGO brought women from slums to the rainwater club and showed them the method. Rooftop rainwater from a small roof of 12 square metre is being collected in a 500 litre HDPE tank. All the women agreed that the idea was simple and would work for their homes too. An inventory of the willing families was done and a cost estimate prepared. A plumber was brought and trained on how to build the system. Five homes now have rooftop rainwater harvesting.

The project is to expand and cover more houses in the near future. This month, in July itself, a significant quantity of rainwater has been collected and all the home owners are happy with the amount and quality of water they have got.

Cost is a critical issue, while the original estimate was Rs 2700, the actual was reported as Rs 3000 per unit.

Advantages of rooftop rainwater harvesting:

It has been clearly established that increased quantity of water use results in health benefits to families. Excepting thatch roofs, all other roofs are amenable to rainwater collection. The technology is simple and should be directed at women to understand since they manage water in their houses. Rain barrels provide much needed supplemental water during the rains and provide a storage system for scarce water during the non rainy days.

Tied to a rooftop improvement scheme, rainwater harvesting improves the quality of the house as well as provides an intervention for better water and sanitation behaviour. People innovate and modify systems to their requirement. For example one household stores water once a week instead of the usual alternate day at 5.00 a.m. in the morning. This reduces drudgery.

Good work by NGO’s like the Rayapuram Slum Development Society will surely be replicated by more NGO’s and CBO’s and water will no longer remain a pipe dream for slums.


RAINWATER HARVESTING IN A HOUSE

Prithvi and Purushottam, twin brothers, bought their 30 feet x 50 feet site in Sahakarnagar off Bellary road in North Bangalore. From the beginning they were keen on incorporating rainwater harvesting in their house design and insisted with the Architect to incorporate it into the plan itself. Roof: The roof area of the house is 650 square feet approximately 65 square metre. The roof was appropriately given a slope during the water proofing course to bring all the rainwater to one point. The rainwater is brought down through one 90 mm diameter down-pipe to a first rain separator. This is a multi-purpose device. When the terrace is being cleaned, the cap of the first rain separator can be opened and the dirty water allowed to flow in to the front garden. After cleaning the cap is closed and the first rain separator collects the first 1.50 mm of rain falling on the terrace every time it rains. The maximum amount of silt and dust on the roof is picked up in this vertical pipe first rain separator leaving cleaner rainwater to be filtered and stored for use.

The first rain separator with an end cap- used as a bye pass when cleaning the roof

FILTER: After this separation, the rainwater is filtered. Purushottam designed the rain filter using a 90 litre blue colored HDPE drum. Rainwater enters from below the drum and passes through two layers of sponge kept at intervals. The water is then picked up at the top and led into the sump tank of capacity 6000 litres.


Rainwater enters the filter from the lower pipe to the left and is picked up by the top

pipe before being led into the sump whose brown cover is seen at the back

During heavy rains if the sump tank fills up, the overflow of rainwater is led into an open well on site. The well water has considerable improved both in quantity and quality over time. Whenever well water is available it is used for all purpose. The house is a ‘zero runoff’ house in so far as rainwater is concerned. All rainwater falling on the plot or the roof is either collected or allowed to recharge into the open well. In fact the side setback area is left unpaved to allow for infiltration of rainwater too. It is estimated that the house harvests around 50,000 litres annually in the sump tank and recharges around 30,000 litres into the well annually from overflows and from the paved area. Ownership: There is great ownership of the idea of rainwater harvesting in the family. The Rain water filter is prominently placed in front of the house to explaining the mechanism and benefits to curious relatives and friends. The system works exquisitely only when it is taken under the wings of the family.


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