Every drop counts: Plan a rainwater harvesting system based on the rainfall and water usage pattern

Rain water harvesting is collection of rainwater falling onto catchment areas such as roofs, terraces, lawns, pavements etc, into storage tanks, ponds or aquifers. Rainwater harvesting is an age-old concept, which provides a solution to the problem of increasing water demand by increasing ground water levels. It also helps in controlling the water run off into drains and mitigates resulting water logging problems.

Rainwater can be harvested from rooftops, paved and unpaved areas, lawns and the water can be stored for meeting the various demands of a building for applications such as flushing, cooling, watering the landscape and so on. An annual rainfall of 611mm would result in a yearly rain water collection of 52 kilo litres for a building with roof area of 100 sq mtr in a city like Delhi.

While planning for a rainwater harvesting system, certain measures/ recommendations should be considered.

It is advisable to plan for storage of rainwater based on the rainfall and water usage pattern.

For example, if the rainy season lasts for more than four months, a storage system to capture rainwater is recommended.

Otherwise it is preferable to recharge the aquifer with the harvested rainwater. The soil and subsoil condition of the site are important if a recharging system is planned. The run-off can be arrested and the infiltration of water into the ground improved by increasing the vegetative areas of the site.

Rainwater is essentially bacteriologically pure, free from organic matter and soft in nature. However, care should be taken to ensure its quality during storage.