Section 4(6) in Tamil Nadu Panchayats Building Rules, 1997
(6)For effective conservation of rain water, no approval to the construction or addition or alteration to a building (other than a hut) including houses constructed by Government for below poverty line families under the poverty alleviation programmes or building constructed by any agency under the control of the Government, shall be given if the application for construction, re-construction, alteration or addition to such a building does not contain provision for water conservation and rainwater harvesting as specified below: -(A)Tiled and sloped terrace building. - (1) In the tiled or sloped building, semi circular gutters of width 15 to 25 centimetres of plastic or any other material shall be provided on the down side roof slopes of the building for harvesting rain water. The gutter shall be connected at the down stream end with a down pipe of 75 to 100 millimetres diameter, depending upon roof area and size of tank to convey the harvested rainwater from gutters to a plastic or other material storage tank or sump (through a filter unit). An inlet screen (wire mesh to prevent entry of dry leaves and other debris into the down-pipe shall be fitted. The collected rainwater from the roof shall be allowed to pass through a filter unit. The filter unit shall be filled with suitable filter material such as well-burnt broken bricks (or pebbles) up to 5 centimetres from top. The top 15 centimetres shall be filled up with coarse sand. The filter unit shall be placed either over a storage tank or at bottom of the down pipe.
