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Rain water harvesting yields rich dividends

A study of Chennai Metrowater shows that there has been a 50 per cent rise in water level in the last five years and the water quality has significantly improved , writes K. Lakshmi
When Jamuna Raman bought a house in Villivakkam six years ago, she had to spend a significant amount on digging a borewell for nearly 150 feet deep only to taste saline water.
Now, she and her counterparts in the area enjoy better water quality, thanks to rainwater harvesting system (RWH) adopted in many households.
“Earlier, I had to depend entirely on the piped water supply and private water tankers for all water needs, including bathing purposes. Now, I am able to use ground water for non-potable purposes as I had harvested rainwater,” said Ms.Raman.
Many others too have benefited from the regular maintenance of their RWH structures.
The Chennai Metrowater’s study of 759 RWH observatory wells show that ever since the installation of RWH structures in about 5 lakh consumer households was made mandatory five years ago, there has been a 50 per cent rise in the water level .
Improved water level
According to the Metrowater officials, over the last five years, the water level across the city has gone up by three to six metres.
Similarly, the water quality in several areas has also showed improvement.
The sustained normal rainfall since 2004 and the proper maintenance of RWH structures in most households have been the principal reasons.
Following the drought period in 2003 when Chennai received only about 690 mm of rainfall as against its normal of 1,200 mm, the water table had receded and, on an average, was at 7-8 metres below ground.
In places like Villivakkam it was at 13 m depth and in Vadapalani, Velachery and Guindy it was at 10 m.
Following a good rain (2,064 mm) in 2005 and rainwater harvesting, the ground water table saw an appreciable rise in several areas and the water table reached 1 m depth below ground.
The water level in areas such as Vadapalani and Villivakkam increased and reached 1.30 m below ground and the levels in coastal areas such as Besant Nagar and Santhome rose to 1-2 m. Similarly, the quality of water, which had its total dissolved solids (TDS) as high as 4,900 parts per million (ppm) in areas such as Chintadripet, dropped to permissible levels of 500 ppm.
Before the onset of every monsoon, the Metrowater officials conduct a random check of the RWH structures for their maintenance and create awareness about the need for maintenance. These have paid rich dividends. Government buildings
However, RWH experts note that the many households are now not keen to maintain the RWH structures as they are supplied with sufficient drinking water.
The condition of RWH structures in many government buildings are in bad shape and in dire need of maintenance.
Harnessing water in public spaces and roads that otherwise drained into sea was also neglected in the city, many complain.
But, officials of Public Works Department (Buildings) say that engineers deployed in each of the buildings regularly inspect the RWH structures and maintain them.
PWD spends considerable amount on construction of RWH system and a portion of the government grant is spent on RWH maintenance.
For instance, if Rs.1 crore is sanctioned towards a building, about Rs.50,000-Rs.1 lakh is spent on RWH structures.
“We try to maintain the structures within the grant provided to us. The changes in water level and quality are also being monitored in such constructions,” said an official.
Sekhar Raghavan, Director of Rain Centre, Mandavelipakkam, said recharge wells are easier for maintenance than recharge pits which have a smaller diameter.
Harnessing of rainwater that get collected in storm water drain network would help in reducing the inundation on roads and large volume of water draining into sea every year.
A dwarf wall could be constructed to intercept the flow of water and be diverted to adjacent open spaces such as educational institutions, playgrounds and parks.
The method was experimented in Defence Colony, Nandambakkam, eight years ago and has proved to be successful.
The dwarf walls were built in regular intervals in the storm water drain network and linked to recharge wells.
Unless rainwater runoff in both public and private space in the city is harnessed, Chennai may lose out on the precious resource and may end up with water problem during summer months, note rain water experts.