What do you like to do when it rains? Take a monsoon shower? Sail a paper boat with your friend? Watch the rain while enjoying hot samosas and a cup of tea? Have you noticed what your parents or grandparents do? Apart from appreciating a good spell, they place a bucket or a barrel in the verandah or balcony to collect the rainwater. “We could use it to water our plants, you see!” Haven’t you heard your grandparents say? They have just passed on a valuable lesson of harvesting rainwater – collecting and storing rainwater for later use.

Though water is a renewable resource, it is scarce. Hence it is important we conserve water in every possible way.

While parts of India receive heavy rainfall, leading to floods, many other places face acute water shortage every year affecting agriculture, industries and daily life for millions of people. A recent report by NITI Aayog, a policy think tank of the Government of India, says that India faces the worst water crisis in its history, with 21 cities expected to run out of groundwater by 2020. It has also said that about 40% of our population will have no access to drinking water by 2030. In the face of such a grim future, it’s important to know what we as citizens can do to store and utilise rainwater.

Rainwater harvesting

Most of the time, the rainwater that falls on our roof and concrete corridors flows through gutters and downspouts and becomes runoff. By installing a rainwater harvesting system, you can not only capture rainwater and store it for later use, but also recharge the groundwater.

They can be installed anywhere – in houses, offices, parks, and schools. The advantages include reduction of urban flooding, recharging of local aquifer (such as wells), and most importantly ensuring water availability in water-scarce zones. By using stored rainwater, the stress on underground water can be minimised.

Rainwater harvesting involves the collection of water in container – a barrel or a underground tank – and using it for various purposes.

A rainwater system basically consists of …

A water storage or holding tank
to store the water collected from the roof or other surfaces. It can be cisterns, large tanks installed below the ground or tanks at the side of the house or building.

A filter
to strain debris in the water (such as leaves and dirt) from entering the water tank. Different levels of filtering, such as gravel, sand and netlon mesh filters, are required depending on the eventual use of the collected water.

A pump
to direct the water to where it needs to be used. Pump is a necessity for systems buried underground.

There are different methods to rainwater harvesting.

Two basic methods

Rooftop rainwater harvesting

Surface runoff harvesting

Rooftop method

1. The simplest rainwater harvesting is to divert the downspout from your roof directly into your garden.

2. Rainwater that falls on the rooftop can be made to run through a pipe to a storage facility such as a barrel or sump or a tank. This water can be filtered to purify the larger particles before being stored in tanks.

Surface runoff harvesting

This method helps in recharging groundwater aquifer, where water moves downward from surface water to groundwater. This can be achieved both naturally and through artificial groundwater recharge facility, where rainwater is routed to the subsurface. The harvesting structures should ensure percolation of rainwater in the ground instead of draining away from the surface. By this, we can recharge borewells, dug wells, pits, trench and percolation tanks.

Direct storage

A rain saucer, with a structure like an upside-down umbrella, captures rainwater straight from the sky and fills the containers. The water thus stored is less contaminated.

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