Section 5A(2)(b) in The Chennai Metropolitan Area Groundwater (Regulation) Rules, 1988
(b)surface run-off water from the open spaces around the buildings, parks and playgrounds shall be harvested using appropriate recharge structures based on the nature of the sub-soil conditions.(i)Roof-top rain water harvesting. - Direct collection. - Rain water from the roof of the buildings such as tiled/ sloped terrace building and fiat/ RCC (Reinforced concrete cement) roof shall be collected using appropriate size of gutters or PVC (Poly vinyl chloride) pipes and stored either in a collection tank or storage tank of appropriate size placed over the ground or underground through a filter unit. A filter chamber of appropriate size shall be provided to filter the dust particles usually present in the roof-tops of the buildings. Suitable filter material such as well burnt broken bricks or coarse sand or small sized pebbles or blue metal gravels (baby chips) shall be used in the filter chamber. The surplus water available after filling the storage tank/ sump shall be diverted to the nearby open well or bore well or-recharge pits. Proper disinfection shall be made while storing the water for long use.