5. The ground water scenario in Chennai

Till the early fifties of this century, the citizens of Chennai did not depend on the supply from the CMWSSB as much as they tend to do now. Their needs were met substantially by the shallow open wells that formed an integral part of most households. These were fed by the direct absorption of rain water by the soil and yielded potable water. The city also had a considerable number of tanks - temple tanks as well as public tanks - which were fed by the storm water drainage system in the areas surrounding them. These in turn helped saturate the sub-surface soil in the area with water, enabling the shallow wells in their vicinity to service the needs of the citizens. But, as construction in the city proliferated to cater to the needs of its constantly rising population, the quantity of ground water tapped increased steadily even as the soil available for direct absorption of rain water shrank steadily. The drainage system feeding the tanks fell into neglect and the tanks went dry. Several public tanks were filled up and buildings constructed on them. As a result of all this, the ground water table in the city steadily went down. Because of the lowering of the ground water table, shallow open wells went dry and new shallow wells did not yield. People started tapping deeper layers of the soil for their water needs. Bore wells thus came into fashion. While the deeper bore wells yielded attractive quantities, the quality of water tapped was more often than not unfit for drinking. Consequently, dependence on the CMWSSB for treated potable water sharply increased. However, this tapping of water from bore wells without any corresponding replenishment of the ground water table is also perilous: for, it will inevitably lead to the bore wells also drying up progressively. In coastal areas, the bore wells may not dry up but sea water intrusion will result and the bore well water would become increasingly saline and unfit for most uses. If therefore we have to avoid this perilous future and ensure for ourselves the continued availability of water of satisfactory quality to meet our needs, we have to know more about water management at the local level and reduce our dependence on treated water supply. To do so, let us first look at the inter relationship between soil and water.