Water Blues & Rainwater harvesting.


Water is a perennial problem in most Indian cities. This year it has been even more acute with the monsoon not being so good. It is a big wonder why this should be such a big problem, considering the amount of rainfall most cities get in India.

Calculations will make it much clearer. In India, an average urban dweller needs about 200liters of water for drinking + sanitation. This amounts to 73,000 liters of water per year.

Annual rainfall in Bangalore ranges between 850-900mm.   sq.meter x rainfall (in mm) can give us total annual water received for a given area.  1sq.meter = 10.72 sq.ft. So,  (1/10.72 * 850 ) will give us the amount of water a square foot received in a year in Bangalore. That amounts to close to 80 liters of water per square foot.

A person in Bangalore needs about 73,000/80 sq.ft of cachment area. That is about 913 sq.ft of area per person.

Bangalore is estimated to have a population density of about 7500 people / sq. km. Since one sq.km is about 10,763,910 sq. ft –  per person land availability is about 1,435sq.ft. in the city limits. Clearly, enough rainwater is received within the city for human consumption and some more for upkeep of the city’s gardens. In addition, Bangalore is close to larger catchment area of Cauvery. So,all it needs is an efficient way of storing and distributing this rain water.

While at city level things may not happen or may take a long time, at personal level  people can certainly do something about this. One simple thing people are doing is rainwater harvesting. One can calculate how much rainwater a residential property can generate.

A 2,400sq.ft area can receive more than 150,000liters of rain water per year. Storing this efficiently can provide enough wanter for 2 people throughout the year! Or enough water for a family of 4 for more than half year.

I believe all future housing projects should be forced to have a mechanism to store all the rainwater they receive. It isn’t too difficult.  For example – to store 150,000liters of water, about 6,000 cubic feet of storage area is needed. That’s 1000sq.ft area * 6 feet deep.With efficient, non-concrete storage, that only gets filtered water and no sun rays, won’t permit growth of Algae and other organic stuff.

Doing this efficiently can easily bring down water requirements from the rivers by half. In future, if we can also adopt good water recycling mechanism, cities like Bangalore can be self sufficient in water.