Water Harvesting
Wg Cdr (Retd) J Thomas
(copied from which will cease to exist very soon. neverthless the information provided is valuable and needs to live on)

Bangalore has a population of 6 – 8 million which is growing rapidly. The per capita income is also rising and this puts a further strain on water resources. Bangalore does not have a river flowing closeby. Historically, it has relied on ground water augmented by two dams — Heserghatta and Thippagondanahalli – on the Arkavati river. The Arkavati is a minor river originating in the Nandi hills and flows into the Kaveri. Both these dams used to have sufficient water for Bangalore but, due to increasing use of ground water for agricultural use in the catchment area, they are now dry for most of the year. Over the past three decades, Bangalore has resorted to the costly method of pumping water from the Kaveri river which is about 100 km away.

Almost all the open wells in Bangalore and neighbourhood have become dry. People are now dependent on bore wells which go down anywhere between 400 and 1000 feet. As the water table goes down, many bore wells run dry. If the bores are surrounded by built up area, it is not possible to deepen them and people are increasingly dependent on water supply through tankers. Many households now spend more money on raw water than on milk or petrol.

The rural areas of Karnataka are supplied free or subsidized power. The result is that farmers run their bore wells whenever power is available. They even dig bore wells on lakebeds and river beds with submersible pumps fitted at the bottom. These are encased in concrete and the pipes and electrical conduits run underground. They are virtually undetectable. As a result, the water table in rural areas around Bangalore has dropped to 1,000 feet with no improvement in sight.

There are several major ongoing infrastructure projects “benefiting” Bangalore. These include the new international airport, the Golden Quadrilateral and North South highways, Metro rail, third rail terminus, Mysore highway and peripheral ring road. Satellite towns like Whitefield, Hosur and Yelahanka are developing and becoming part of Bangalore. These infrastructure projects will only give temporary relief, because they act as magnets for more migration from the small towns and rural areas.

Water supply is, and will continue to be, the major problem in Bangalore. We have been assured Kaveri water supply. But, given the past track record, this assurance is not credible. Moreover, when the water situation gets worse, the farmers will simply cut the Kaveri pipeline and take the water.

It is bad enough that ground water in Bangalore has salt (sodium chloride) in it. What makes it positively dangerous are the industrial chemicals and heavy metals that are in the ground water. These damage the body organs, especially the kidneys. Our future generations are at risk.

Bangalore gets about 1000 mm (40 inches) of rainfall on the average. Fortunately, this is mostly spread over the eight months April to November. Conditions are, therefore, favourable for water harvesting. Apart from cost savings, we get the added benefit of pure water which is essential for our children’s health, conceding that we retired folks are beyond economical repair.

The government has made water harvesting compulsory in Bangalore. But they will be satisfied if we dig a few recharge holes in the ground. This will recharge the ground water in a general sense but does not provide us any direct benefit. We should, therefore, go in for direct methods where we fully utilize the precious rainwater that falls on our property.

Direct Collection in Sumps

Rainwater falling on the roofs can be collected in a sump below the floor of the building or adjacent to it. Online filters for the pipes are available. The water so collected is pure and can be directly used for pumping into the overhead tanks. There is a small government office that offers free advice on water harvesting. Contact person is Mr Farooqui, phone 080-2666 5720

Direct Collection in Wells

Rainwater falling on the ground can be channeled into a filtration tank and then fed into a well. A simple sand filter will do. If the well is lined with cement concrete, the water will be stored for a longer time. Provided there are no significant quantities of harmful chemicals in the soil (chemical fertilizers etc), this water can also be used for cooking and drinking. It can be pumped into our overhead tanks.

This water can also be used for our swimming pool. BTW, solar heating can make our swimming pool usable throughout the year.

Recharge into the Ground

The recharge pits are unlined and allow the water to soak into the soil. This raises the water table in the general area. It also benefits the trees which have deep roots. We should employ this method for the excess water that overflows from the sumps and wells during periods of heavy rainfall.

Contour Bunds

When laying out the gardens, we should make terraces and make low bunds that follow the contours. This would hold back the rainwater and let it soak into the ground.

Recycling of Sewage Water

In the days when chemicals were in less widespread use, a simple septic tank was enough to purify sewage to the level where it could be used for gardening. However, now we have heavy use of soaps and detergents, as well as various chemicals that are discharged into the sewage outlets. We, therefore, probably need a mini sewage treatment plant.

This sewage plant will perforce be at one of the lowest points in our property. The treated water should flow into a tank from where it can be pumped up for gardening. The solid output can be used as manure for gardening.

The Stream Through our Property

There is a stream that flows through our property. It carries both rainwater and sewage. It contains far too much sewage and chemicals for us to treat economically. It may, therefore, be allowed to pass through unhindered. The project plans call for covering this stream.

Cost Benefit

Some members have not been taking interest in the project because they do not intend living in the flats. This place may be their second or third property. They intend renting out the flats and, possibly, selling them after some years. Such members should note that their property will fetch a higher rent and a higher sale price if the surroundings are well developed and if the campus has good facilities.

As far as water harvesting is concerned, it is to get potable water which is an essential commodity. The alternative is to buy raw water in tankers which is very expensive.

The only part of the water harvesting project that needs a cost benefit analysis is the mini sewage treatment plant.

See Also

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