Groundwater plays an important role in meeting end use demand by household and industries. However, with the growing population of Chennai and Uncontrolled utilization of groundwater has also led to its rapid decline in the city. This uncontrolled usage occurs both within and outside the city limits. Climate change leading to uneven rainfall and severe drought has also impacted the groundwater table severely. Within city limits, groundwater extraction takes place from about 0.42 million private groundwater wells, with 66% of households having their own private wells. The water table is not uniform throughout and is dependent upon hydrogeological patterns. The stretch along Ennore to Sholinganallur along the sea coast has a coastal aquifer which stores water. Here it is brackish saltwater and during over extraction, intrusion of seawater occurs. As saltwater moves inland, it makes an impact on groundwater quality. Hence groundwater is not of good quality along Coastal Chennai. Central Chennai has rich alluvium deposits, through which Adyar and Cooum river flows. The area is effective in storing water due to the porosity of alluvium. South Chennai has a rocky terrain, made of hard rock aquifers and water storage is less in this area. Western Chennai has limited alluvium, followed by clayey soil, rendering groundwater with high iron content unsuitable for consumption. North Chennai has sedimentary rocks, with layers of sandstone and sand or shale, making it conducive for consumption.
