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Rainwater harvesting in Bangalore

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By S Vishwanath

With groundwater levels fast depleting, rooftop rainwater harvesting makes sound ecological and financial sense. Bangalore seems to have taken the lead in this form of water harvesting and has even set up a special Rainwater Club

Bangalore's Rainwater Club, started in 1995, consists of a group of architects and engineers who focus on incorporating rainwater-harvesting (RWH) techniques into buildings. They feel that although the concept of rainwater harvesting is becoming popular, policy-makers, architects, engineers and the general public need to be made more aware of the method.

Since rainwater harvesting is related to the soil profile and hydrogeology of any given area, specific methods have to be developed for specific sites. A one-size-fits-all approach will not work. Demonstrations of such simple techniques as recharge pits in minor drains that are not polluted with wastewater, can be arranged on a case-to-case basis in many localities. The recharge of open wells and borewells from rooftops should be encouraged, as most cities have such wells. Bangalore itself has more than one lakh wells!

With help from Rotary North-West, the Rainwater Club has come out with a booklet, in English and in Kannada, which explains the basics of rooftop rainwater harvesting and also provides rainfall data on each district in Karnataka, to enable citizens to design rooftop rainwater harvesting systems for their specific location. A website www.rainwaterclub.org has also been launched.

Meanwhile, students at several colleges in Bangalore are being taught rainwater-harvesting techniques. The students of MVJ College of Engineering, Whitefield, have, in fact, designed an excellent rainwater harvesting system for their campus; it is seriously being considered for implementation. The Rainwater Club also presents slideshows at resident welfare associations, to NGOs, rotary clubs and the general public.

All this has prompted a number of individuals in Bangalore to implement rainwater harvesting in their own localities. And the results have been encouraging.

Balachander Pai, who lives at Shandilya Apartments, Malleswaram, 7th Cross, decided to try out rooftop rainwater harvesting, with a little help from the club. Rainwater is filtered and harvested from a roof area of 1,000 square feet, and channelled into an open well. From 400 square feet, rainwater is filtered and led into a borewell through an indirect recharge pit. Approximately 1,20,000 litres of rainwater will be harvested and
recharged at this site, every year.

The project's cost was a mere Rs 18,500! Since the
building has eight flats, each flat owner had to pay a sum of Rs 2,312 towards the project. Over 50 years (the project's lifecycle), the amount of rainwater that is harvested will be 60 lakh litres. This huge amount of water will be saved from going waste and adding to urban flooding.

Similarly, Dr Gopalkrishna Rao, another Bangalore resident, too has opted for rainwater harvesting. His house, in UAS Layout, Sanjaynagar, incorporates a system wherein rainwater is collected from the rooftop (nearly 1,000 square feet of it), filtered and led into a sump. There is also an alternative arrangement to recharge an open well which went dry after 20 years. At a project cost of around Rs 6,000, Rao's system is expected to harvest nearly 90,000 litres of water every year.

Rainwater harvesting may be incorporated into a building's design at an early stage, as was the case with Kunjithapatham and Pushpa's house located at 6th Block, BEL Layout, Vidyaranyapura. Rainwater from the rooftop is led into a rainwater filter tank built out of ferro-cement. This filter tank doubles as a sitting place and a nice area for flowerpots. Water is then led from the filter into a sump.

Pradeep and Pushpa, who also live in Vidyaranyapura, are innovative rainwater harvesters. Instead of using conventional pipes, their architect, Chitra Vishwanath, designed a system of hanging chains which bring rainwater down by surface tension! Thus, the water descending from the roof can be both seen and heard, adding an element of enchantment to the house.

Industries in Bangalore that have started harvesting rainwater include Escorts, at Yelahanka, and Denso-Kirloskar near Nelamangala. Other companies like MICO, AISIN-NTTF, Ingersoll-Rand and ITC are also actively considering incorporating rainwater-harvesting systems.

In order to popularise the concept of rooftop rainwater harvesting there are several areas that require attention. The need to develop a quick, low-cost and easy system of checking the quality of rainwater run-off, at selected laboratories; developing affordable filters to improve the quality of rooftop rainwater; offering a monthly rebate in water charges, by the government, to rainwater harvesters; setting up professional information cells, by water supply and sewerage boards, to answer people's queries; creating a trained pool of plumbers and masons with rainwater harvesting know-how and training borewell diggers in recharging techniques.

A flat roof should be gently sloped to allow for easy drainage towards the storage system. While casting the roof, a `nahani trap' or `floor-trap' may be placed near the inlets to the downwater pipes. Sloping roofs should have a PVC gutter or a zinc sheet that collects water and channels it to the downwater pipe system. Roofs should be left uncluttered and should be easy to sweep and swab clean if necessary. 90mm diameter PVC pipes, that are resistant to UV rays, appear to be the best bet for downwater pipes. This, of course, depends upon the roof area to be drained. Three to four downwater pipes are sufficient for a 1,000-1,200-square-foot area. Filtering can be as basic as a floor-trap placed before the entrance to the downwater pipes, or a piece of sponge placed at the inlet to the downwater pipes. A PVC bucket with gravel, sand and charcoal makes a good filter. A PVC drum with a sponge at the inlet and outlet also makes a good filter. A small two-chamber inspection/filter tank may also be devised. Try to determine your water harvesting system at the planning stage itself. It could be: A roof-level storage tank. A ground-level drum or masonry tank. An underground sump. A partially underground tank. Roof-level storage tanks may need to be at the rear of the house, or along the sides, so that they are neither obtrusive nor visually offensive. Ground-level drums or tanks occupy space. They should not hinder movement or appear unsightly. Below-the-ground sumps are a good option as most new constructions go in for sumps anyway. Sumps are concealed and less costly to build. They also do not obstruct movement. Always provide for an outlet for any excess collection of water in the storage system.

(S Vishwanath is a Bangalore-based urban planner. He is the founder of the Rainwater Club)

Signs of Hope, September 2002