The average ground water level in the city rose by 0.80 metres due to
implementation of rainwater harvesting, according to Chennai Metro
Water.

A Chennai Metro Water report said the water level was 4.20
metre from the surface, but after the rain water harvesting, the water
level had risen to the level of 3.20 metre from the surface.

The
ground water levels in Tiruvotiyur, Manali, Madhavaram, Tondiarpet,
Royapuram, Thiru-Vi-Ka Nagar, Ambattur, Anna Nagar, Teynampet,
Kodambakkam, Valasaravakkam, Alandur, Adyar, Perungudi and
Sholinganallur had improved the report said. The ground water level in
Alandur which was 7.45 metres deep before monsoon rose to 4.80 metres
due to rain water harvesting, it said. It also said the groundwater
quality, which gives a measure of the total dissolved solids had also
improved in the range of 500 to 1700 particles per cubic metre.

Interestingly,
this comes after the city installed eight lakh rain water harvesting
structures. Besides, the Chennai Metropolitan Development Authority
plans to carry out rainwater harvesting audit though a network of NGOs,
who pioneered in this field.

The biggest challenge for ground
water depletion is heavy extraction of ground water. According to
estimates, the city requires 1100 mld of water a day while Metro Water
supplies around 830 MLD a day. As such nearly 300 mld of water is
extracted from the ground.