Rainwater harvesting (RWH) has evolved as a model to conserve water and also to effectively discharge used water back into the ground; thereby recharging the water tables and keeping them accessible. Urban environmentalist Indukanth Ragade from Chennai and Shubha Ramachandran, Water Sustainability Consultant with Biome Environmental Trust, Bangalore, share the total perspective on RWH with the systems and models in use in Chennai and Bangalore respectively, with Vijayalakshmi Sridhar.
In the olden days, with the ground well being the sole water source and recharge point, a cyclic movement of water within the plot is initiated so that rainwater is harvested and used water is redirected into the ground or well. Therefore, each household was self-sufficient in its water requirement and usage. The same model was applied across villages, panchayats and towns keeping them well supplied throughout the wet and dry seasons.
However, with increasing population, migration to cities, modern town planning and the municipal water supply cut the dependence on wells. Resultantly, the household used water flowed into the central sewerage system. Since there was no movement of water back to the soil or the water source, the wells dried up and water tables sunk deeper. Sadly, the demand has multiplied and now is the time for us to revisit the old methods.
“The only way to avoid a consequent urban water crisis is to try and revive the earlier circular movement of water as much as possible,” says Indukanth Ragade. Ragade’s comprehensive system involves harvesting each drop of water that falls within a residential premise and diverting it to a single source, possibly to a well. This includes the rainwater from the terrace through pipelines, the water falling on the open spaces around the building and the water that falls on the paved driveways of apartment complexes that gets cleaned as it passes through the ground. In some projects, Ragade has worked to divert the terrace water to a sump and the overflow from the sump to the well. “The shallow dug wells provided in more than 150 four-storeyed complexes, built by the company of which I was a part of, are serving the residents well as they are sustained by all the rainwater falling in the premises,” Ragade cites proof to his point.
In Shubha Ramachandran’s view, rainwater harvesting has to be seen in a case to case basis for it to be a viable solution to meet the regular and rising demand for water. “At the household level, trapping and using all the rainwater that falls on the plot, brings in a kind of water autonomy. In fact, coupled with some other measures, it can give 100 per cent autonomy.”
Bangalore’s dependence on wells stopped when the communities switched to the Cauvery water supply. The city gets about 970mm of rain every year, and 70-80 thousand litres of rainwater and household harvesting can see through the water demand for a family of four for about four months on the assumption that the consumption is 600 litres per day (135 litres per capita per day).
Ramachandran explains how ground wells can be used as a reliable source for large scale RWH. “On a city scale, in a large plot of several acres, recharge wells can be dug and this can improve the water quality in the locality and bring up the water tables too.”
Water scarcity could be curtailed by establishing a good water economy by allocating more accountability to usage, such as metering individual and community usage and also substantiating these measures with the available stock of water.