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WATER WISE

Rain tanks for harvesting

S. VISWANATH

With 60 rainy days in Bangalore, a 500-litre tank fixed to a 50-square metre roof catchment can collect nearly 23,000 litres of water in a year



SIMPLE TECHNOLOGY: A rain tank can be placed on any kind of roofing, be it a sloping one or in lawns for industries

The eighth article in our RWH series in this column brings you some simple methods of collecting rainwater in tanks with modest filtration techniques. For now we only have to hope for the best of wet days ahead, as Bangalore needs some heav y downpours for addressing the parched agricultural fields and of course the drinking water needs.

The first step is always the most difficult in beginning any new process and that is true for harvesting rain too. What is then the easiest way to begin?

The rain tank or rain barrel is perhaps the quickest way to harvesting rain. Remember, rainwater harvesting is collecting and storing rain for future use. So how does a rain drum look?

It is nothing but a HDPE tank, the blue and black variety you see everywhere, modified to collect rainwater. People refer to it as a plastic tank or by a brand name but in actuality this is made to store potable water and is U.V. stabilised to prevent it from cracking up when placed in the sun.

Usually flat roofs have down pipes bringing rainwater from the rooftop to the ground to be let out to storm water drains. This pipe is closed with a valve or even a simple end cap. A T-junction is then made at about a height of 8 feet and water lead into the rain tank. Sloping roofs will need to have a rain gutter and a down pipe to bring the rainwater down.

The tank is placed on a small platform about 18 inches high and a tap is attached to it at the bottom. This makes it easy to collect water in a bucket.

First rain separator/bye-pass

This is the vertical pipe with the end cap or a valve. In case of the roof having to be cleaned, the end cap or the valve can be opened and dirty water allowed to flow out into the ground. When the valve is closed, water fills up in the vertical pipe and flows out of the T-junction at a height into the tank.

The filter itself is very simply done by removing the conventional cover of the tank and replacing it with a perforated basin. A net or cloth is placed on this perforation to filter out leaves, dust and other material.The cover prevents mosquitoes and insects from entering the tank as well. The cloth can be taken out and washed whenever dirty with other clothes and is very easy to maintain.

Perforated cover

Where can the rain tank be placed? Many people prefer to place it on the terrace. It can be placed on the ground where the down pipes come too. Small houses find space literally on the pavement. Apartments find niches to place the rain tank and use the rainwater for gardening. It needs a small space of about 3 feet x 3 feet.

How much water can we harvest?

A surprisingly large volume can be harvested for even a small tank. For example, in Bangalore city with around 60 rainy days, a 500-litre rain tank fixed to a 50-square metre roof catchment can collect nearly 23,000 litres of rain in a year. This is provided the rainwater is used up every time it collects rain.

What about the quality of the water? It is wise to check the quality of the rainwater in a laboratory or using h2s strip test bottle.

Where the catchment is kept clean and the filter cleaned regularly the rainwater has been found to be of drinkable quality.

In any case it can be used for gardening, car washing and other sundry non-potable purposes.

With the tap attached to the rain tank, a hose pipe can draw the water and with a good filter this rainwater can be recharged into a borewell or put into a sump tank.

As things go along and if one is happy with the performance of the rain tank, another one can be added parallel to it. To make a beginning is difficult, ‘starting trouble’ as we famously say in India.

A rain tank can be fitted within half-a-day by a plumber and requires absolutely no expertise.

So, why don’t you consider installing one today and overcome the starting trouble? The bulk of rain in Bangalore is yet to arrive and we can raise a toast to the drops of collected rainwater.

www.rainwaterclub.orgwww.arghyam.org

Ph: 41610190

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