Just a correction. Only houses in chennai are doing rain water harvesting. Saving water in houses is a very small deal, the big deal comes from when you can store water in lakes, tanks etc, diverting rain water to properly flow into the tanks..
Also, Koovam turns into sewage only after it comes near Chennai, it is a pure water source at the place where it originates (200kms from Chennai) Please remember that living started in Chennai (or chennarayapattinam)on the banks of this river (tributary).
