3.4. Rooftop Rainwater Harvesting in India

In semi-arid and arid regions of Rajasthan, particularly in Bikaner, Phalodi, and Barmer, almost all the houses traditionally had underground tanks or tankas for storing drinking water. The tanks could be as large as a big room; one household in Phalodi had a tank that was 6.1 metres deep, 4.27 metres long and 2.44 metres wide. The tankas were part of the well-developed rooftop rainwater harvesting system and were built inside the main house or the courtyard. They were connected to the sloping roofs of the houses through a pipe. Rain falling on the rooftops would travel down the pipe and was stored in these underground ‘tankas’. The first spell of rain was usually not collected as this would clean the roofs and the pipes. The rainwater from the subsequent showers was then collected.

In Rajasthan, people have developed a unique method to collect and store rainwater through rooftop harvesting. Many houses are equipped with underground tanks, known as tankas. These tankas are designed to capture rainwater that flows from rooftops during the rainy season. The purpose of these tanks is to provide a reliable source of drinking water, especially important in dry seasons. To ensure clean water, the first rain is often not collected to wash away any debris from the roof. Instead, water from the following rains is stored, making it safe and clean for drinking water.

Think of it like a funnel collecting rainwater from a roof into a big bucket. The first few drops are used to clean the funnel, and once it's clean, the water collected after that is pure and ready to drink. Just as we use a funnel and a bucket for collecting water, the tankas serve a similar purpose but are built underground to keep the water cool and fresh.

Tamil Nadu is the first state in India which has made rooftop rainwater harvesting structure compulsory to all the houses across the state. There are legal provisions to punish the defaulters. Rooftop rainwater harvesting is the most common practice in Shillong, Meghalaya. It is interesting because Cherapunjee and Mawsynram situated at a distance of 55 km from Shillong receive the highest rainfall in the world, yet the state capital Shillong faces acute shortage of water. Nearly every household in the city has a rooftop rainwater harvesting structure. Nearly 15-25 per cent of the total water requirement of the household comes from rooftop water harvesting.

To encourage the conservation of water, Tamil Nadu has implemented a law that requires houses to have rooftop rainwater harvesting systems. This means that every homeowner must collect and store rainwater. In Shillong, despite being located near areas with very high rainfall, water scarcity is a problem. However, to mitigate this, almost every household uses rooftop harvesting to meet their water needs. This measure allows them to collect a significant portion of their water supply from rain, demonstrating the effectiveness of such systems.

It's similar to a school rule requiring students to bring reusable water bottles to reduce waste. Just as students must follow this rule to help conserve resources, homeowners in Tamil Nadu must install rainwater systems to help manage water scarcity. In Shillong, even with so much rain around, having these systems means that families can solve their water problems by using what nature provides.

Today, in western Rajasthan, sadly the practice of rooftop rainwater harvesting is on the decline as plenty of water is available due to the perennial Indira Gandhi Canal, though some houses still maintain the tankas since they do not like the taste of tap water. Fortunately, in many parts of rural and urban India, rooftop rainwater harvesting is being successfully adapted to store and conserve water. In Gendathur, a remote backward village in Mysuru, Karnataka, villagers have installed, in their household’s rooftop, rainwater harvesting system to meet their water needs. Nearly 200 households have installed this system and the village has earned the rare distinction of being rich in rainwater. Gendathur receives an annual precipitation of 1,000 mm, and with 80 per cent of collection efficiency and of about 10 fillings, every house can collect and use about 50,000 litres of water annually. From the 200 houses, the net amount of rainwater harvested annually amounts to 1,00,000 litres.

In specific areas of India, while some traditional rainwater harvesting practices are declining due to other available resources, successful initiatives highlight the importance of this practice. Gendathur, a village in Karnataka, has embraced rooftop rainwater harvesting effectively. Here, households have set up systems that allow them to collect rainwater, providing them with a substantial amount of water each year, showcasing how local communities can adapt and thrive despite water challenges.

This is like a group project in school where students share resources and help each other. In Gendathur, families come together to collect rainwater, much like pooling resources for a project. Their joint effort ensures that everyone has enough water, making the village as fruitful as a well-coordinated team effort in class.

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