8. Water Management in Alacrity’s complexes

Meteorological records of rainfall over the city (not the catchment areas) for the past thirty six years (from 1960-1995) reveal that only in three years, 1969, 1974 and 1984 have the monsoons failed. These are the only years in which the annual rain fall was below 40 inches. Significantly, the deficiency of rainfall of even these three years has been compensated by the rainfall in the subsequent years. Thus the average rain fall in the City over these 36 years works out to 51 inches, which, if tapped, would amount to a colossal volume of water. This water presently not only runs wastefully into the sea but does so after first flooding the roads in many parts of the city. If this abundant quantity of water falling over the city is tapped and stored by individual households or apartment complexes, not only will roads be considerably free of flooding but they would be moving that much closer to self reliance in their water needs. For instance the 51 inches of water falling over a 2.5 grounds (6000 sq.ft.) plot over a year amounts to 720 KL. If an 8 apartment complex is located on this 2.5 grounds, this can meet the entire needs of the occupants of the 8 apartments for 133 days. While this may look impressive, the question arises: where can all this rain water be stored? The simple answer to this is with Mother Earth. The best place and also the least expensive place to store this water is the soil below us. Since the upper soil layer in most parts of Chennai is clayey in nature, the rain water will not be able to percolate downwards easily to the sandy layers further below. We need therefore an efficient method by which this water is tapped, transferred to this layer for storage and made available for reuse. Alacrity has put into place in all its complexes constructed in the last three years, the following system that not only traps all the rain water and efficiently puts it into the soil but also in many cases makes the water available for use immediately: A shallow open well is dug in the premises and all the water falling on the terrace is channelised through pipes laid below the ground into this well. Since the terraces are quite clean, direct discharge of the rain water into the well is quite safe. If the soil profile is not very favourable for an open well, then a 4 ft diameter pit is dug to a depth of 12 to 20 ft (i.e. until a reasonably sandy stratum of the soil is reached) and the terrace rain water is diverted into it similarly through concealed underground pipes. All the rain water falling on the paved open spaces around the buildings flows towards the road. This is tapped at the gate in a shallow pit provided with grills and the water is led into an absorption pit as in (2) above or into another such pit dug for the purpose. Where a reasonably sandy layer is not likely to be available even upto 20 ft, two or three hand bores are dug in a shallow pit. The pit is filled with pebbles and the pipes in the pit are provided with slotted holes to facilitate the rain water to pass through the pipes into the sub-soil smoothly. Rain water from the set backs is then led into this pit. This arrangement is effective but comparatively costly. If an old well that had dried up exists in the premises it is retained and the terrace rain water pipes are connected to it. Our experience with this arrangement over the last three years has proved conclusively that: the well yield (whether open well or bore well) improves considerably. the water quality improves and salinity decreases steadily. old wells that had dried up are rejuvenated and start yielding again. In fact, Alacrity plans to provide one open shallow well in every complex constructed by it hereafter as it offers the best scope for making available the rain water harvested during the monsoon. Even if such a well is dry initially when dug, it will become a source of water progressively with every monsoon, as a result of rain water harvesting. These measures are not only low in their capital cost but once put in place, operate on their own without any monitoring and without any further expenditure. They also offer prospects of getting potable water from the captive sources sooner or later and eliminate dependence on treated water from outside. Such wells can be covered by an R.C.C. Slab at the ground level so that movement of men and vehicles around the building is not impeded in any way.