A Do It Yourself for the City-bred

Indians, over centuries, developed a range of techniques to harvest rainwater, as part of their daily lives. From the network of copper pipes of the Harappa times, to the intricate network of filtered water supply that some of the Saurashtra kingdoms evolved over 1500 years ago, there has been craft and engineering brought to bear on such urban water planning. Urban rainwater harvesting techniques have been virtually non-existent in all urban planning of the last hundred years.
India has more than 250 million city dwellers. The water supply sector is faced with a number of constraints. Almost all the cities depend on groundwater as a major source. The result is rapid depletion. In addition, the problem of quality is getting grim. Problem of increasing salinity, nitrate, hardness, fluoride is common.
Broadly, rainwater can be harvested for two purposes; storage for direct usage, and for groundwater recharge. If the number of dry days is fewer, then it can be used for direct usage—like in Kerala and Mizoram. This will not work in cities like Delhi or Bangalore, where the recharge option works better, as rains are for a shorter duration.
Suppose, a person has a roof with an area of 100 cubic meters and is getting 100 millimeters of rain—then, his rainfall endowment is 10,000 litres and, the potential is 8,000 litres.
Direct storage is a well-tested technique. The rooftop run-off is taken to storage containers. As per the rain coefficient worked out above, 8,000 litres of water can be used by a family of four members for 200 days. It will fulfil drinking water needs.
To prevent leaves and debris entering the system, mesh filters are used. In some cases, this rooftop harvesting system comprises of commonly used storage containers like masonry or plastic water tanks. Some maintenance measures like cleaning and disinfection are needed to ensure quality of water.
Alternative to storing, rainwater may be charged into the groundwater aquifers. While some structures promote the percolation of water through soil strata at shallower depth [like recharge trenches, permeable pavements, and so on], others conduct water to greater depth from where it joins the groundwater (like recharge wells]. At many locations, existing features like wells, pits and tanks can be modified, eliminating the need to construct afresh—reducing the cost.
There are many shining examples of such saving, and reuse of water from among companies, individual homeowners and institutions.
The power of such techniques is hard to believe. You only have to visit any such place where the recharge system has made a dramatic difference, and you will be impelled into creating them yourself. And the costs are not forbidding.
The road to sanity on water in the years ahead is that each of these monstrous apartment blocks sets up cost-effective sewage treatment systems that can offer you water that’s as good as any water you drink. Only, you may decide to use it for irrigation and flush tanks, which are, in any case, the high-consuming water segments in a house.