Wednesday, January 26, 2022

Go With the Flow: The rainwater harvesting movement is steadily gaining momentum

In India, rainwater harvesting goes back centuries.

Written by S Vishwanath | New Delhi |
July 12, 2015 1:00:26 am
A ferro cement water filler in a Bangalore home A ferro cement water filler in a Bangalore home

Every morning after he has finished his coffee and read his newspaper, Balasubramanian moves to check his open well. A floating ball has been placed in the well and a cord attached to it. It tells the Bangalore resident how much water has risen. “By five feet,” he says happily. Balasubramanian has also placed a blue drum on the well; filled with sand and charcoal, this is a filter for the rooftop rainwater that he collects. The cleaned rainwater is then let into the well gently through a pipe. The rains in June have been good and the well now has 25 ft of water, enough for the whole year, he thinks. This was not the case 10 years ago; the well had gone dry. But rainwater harvesting came to his rescue.

In India, rainwater harvesting goes back centuries. Collecting and storing rainwater for future use has been one way that forts, for example, have managed to survive the sieges laid on them. The tradition possibly evolved in the drier states of Rajasthan and Gujarat where rivers barely flow and groundwater is non-existent. Here, collected rainwater in storage tanks called tankas provided drinking water. Rainwater nourishes the soil and helps crops grow; rainwater in the aquifers help recharge and keep wells alive. In Bhavnagar, Gujarat, I once saw beautiful copper-lined and covered tanks used to harvest rain on the rooftop of a house. The tank were uncovered only after the first rains, which carries silt and dust. Subsequent rains would then fill up the underground tank. The copper lining acted as a bacteria-killer, keeping the water potable.

With the arrival of cheap piped water supply and the easy drilling of bore-wells, the demand for water at a household level has increased. Modern sewage systems also call for large volumes of water.

In 2001, in Chennai, rainwater harvesting took off in a big way. A severe water scarcity had dogged the city for years and alternative sources for water had to be seriously examined. With the city getting an average rainfall of more than 1,000 mm in a year, rainwater harvesting was made compulsory for all houses.

A rainwater harvesting filter A rainwater harvesting filter

Today, Chennai has the largest number of rainwater harvesting systems for any city in the world with over 5,00,000 installations. The practice has become popular in Delhi, Mumbai, Bangalore and Jaipur.

Bangalore modified its building by-laws to make rainwater harvesting compulsory for buildings beyond a certain plinth area and on certain large plot areas. A rainwater guidance centre called the Sir M Visvesvaraya Rainwater Harvesting Theme Park was set up to demonstrate harvesting techniques and to provide citizens guidance on design, cost and also connects them with trained plumbers.

With over 4.5 million open wells, Kerala has the largest density of open wells in the world. A programme named Mazhapolima began in 2008. Taking off from an idea called backwashing of wells, rooftop rainwater is picked up and filtered through a basic cloth filter and let directly into the open well. Also, wells which reported iron or salt in their waters now have sweeter and better quality water. It is estimated that over 80 per cent of rural India gets its drinking water from groundwater, usually deep borewells. Many reasons have contributed to fluoride and arsenic contamination of borewells. More than 66 million people are consuming fluoride-contaminated water and about 18 million people could be consuming arsenic-contaminated water.

In Karnataka, the NGO BIRD-K, has taken up a massive rooftop rainwater harvesting programme, called Sachetana, to give fluoride-free water for cooking and drinking to families. Here, rooftop rainwater is filtered through a sand filtration system and stored in underground sump tanks of capacity ranging from 5,000 to 10,000 litres. This water is drawn up by using a small hand-pump and used exclusively for drinking and cooking. The demand estimated for drinking and cooking is 20 litres a day, the availability of 7,300 litres of rainwater a month can prevent the occurrence of fluorosis and arsenicosis.

The author is with the Biome Environment Trust/Rainwater Club and works on sustainable water and sanitation issues

Save for another day

Why you want to harvest rainwater determines the method. It can be to recharge groundwater and/or store for reuse (potable or non-potable). Costs depends on the quantity one wants to store or recharge, and the type of material used. If you are storing water in underground or over-ground plastic tanks, it will cost you between Rs 2/litre and Rs 3.5/litre. If you choose a ferro-cement tank, costs will range between Rs 12,430 for 5,000 ltr and Rs 15,800 for 10,000 ltr tanks. Installing a water harvesting system can cost between Rs 2,000 and Rs 30,000, for buildings of about 300 sqm, depending on the city you’re in. This estimate is for an existing building; it’s cheaper when done at the construction stage.

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