Section 3A in Tamil Nadu District Municipalities Building Rules, 1972
3A. Water Conservation.
- For effective conservation of rain water, application for permission to construct or reconstruct or alter or add to a building, other than a hut, shall contain water conservation proposals as detailed 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 rainwater. The gutter shall be connected at the downstream end with a downpipe 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 any 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 downpipe shall be fitted. The collected rainwater from the roof shall be allowed to pass through a filter unit. The filter unit is to be filled with suitable filter material such as well-burnt broken bricks (or pebbles) up to 15 centimetres from top. The top 15 centimetres shall be filled up with coarse sand. Tire filter unit shall be placed either over a storage tank or at bottom of the downpipe.(2)The filtered rainwater shall be collected in a collection tank or storage tank placed over the ground or underground. The shape of the tank shall be cylindrical, rectangular or square of suitable size with a capacity ranging from 1,000 to 10,000 litres or even higher depending on the roof area. The materials of construction shall be brick work, stone work, cement bricks, ferro-cement, High Density Polyethylene (HDPE), plain cement concrete or reinforced cement concrete. The storage tanks or collection tanks shall be provided with pipe fixtures at appropriate places to draw the water, to c.e an the tank and to dispose of the excess water depending upon use or reuse either to open-well or bore-well or to a percolation pit.(B)Ordinary building (Ground + First Floor). - (1) Percolation pits of 30 to 45 centimetres diameter and of depth adequate, not less than one metre, to recharge the ground, shall be made. This pit shall be filled with suitable filter materials such as well-burnt broken bricks (or pebbles) up to 15 centimetres from top. The top 15 centimetres shall be filled up with coarse sand. The top of this pit shall be covered with perforated reinforced concrete cement (RCC) slabs or of any other material, wherever considered necessary. The number of such percolation pits shall be provided on the basis of one pit per 30 square metres of available open terrace area or plinth area. The cross distance between the pits shall be minimum 3 metres.(2)Wherever an open-well or bore-well is available within the building premises the rainwater collected from the open terrace shall be collected through pipes of 150 millimetres diameter or other suitable sizes and led to a filter pit of size 60 centimetres x 60 centimetres x 60 centimetres (with appropriate filter materials) and then led into the open-well or bore-well through 150 millimetres diameter or other suitable pipes, after filling up a storage tank or sump.(3)Wherever existing water storage Sumps are available, the rainwater so collected, after it passes through the filter, shall be allowed to flow to the sump through closed pipes. An overflow pipe shall be provided to the storage sump so that the surplus water is led into the nearby open well or bore well or percolation pit.(C)Ordinary building (Ground + 2 floors and above). - (1) The specification detailed in item "B" above for ordinary building (Ground + First floor) is also applicable to building specified in this category.(2)In addition to the percolation pits of 30 centimetres diameter to be provided at 3 metre interval, a pit of 1 to 1.5 metres width and appropriate depth, so as to recharge the ground, shall be provided all along the plinth boundary depending upon the soil classification below ground. This pit shall be filled with appropriate filter material namely, broken bricks, pebbles, broken stones, etc., at the bottom and the top 15 to 25 centimetres shall be filled with coarse sand. The ground or pavement surface around the building shall be sloped towards the percolation pit so that the surplus rainwater from terrace and sides, open spaces, etc., flow over this sloped surfaces and spread into the filter bed all around. Masonry dwarf walls of 5 to 7.5 centimetres or of suitable height depending upon the site conditions shall be constructed, if necessary, at the entrance and exit gates to allow the surplus rainwater collected within the compound to recharge the ground within the premises itself, and from draining out to the road.(3)If the sub-soil is not a permeable one (namely, clay or black cotton) appropriate recharge structures, namely, recharge shaft or bore pit shall be provided below the filtration pits so as to recharge the ground.(D)Group development, industries and institutional building. - (1) For buildings for Ground + First floor or Ground + 2 floors and above located within group development, industrial or institutional premises, the specification detailed in-items A, B and C above shall apply.(2)The surplus surface run off rainwater, in the open spaces within the group development or industrial or institutional premises shall be allowed to rim towards collection drains of suitable size and these drains shall be construed as rainwater-friendly storm-water drains. All the approach and access roads to the buildings within the group development or industrial or institutional premises shall also be provided with rainwater friendly storm-water drains. These rainwater friendly storm-water drains shall not have paved bottom. If adequate spaces are available in low lying areas, percolation ponds of suitable size shall be formed and these rainwater friendly storm-water drains shall be led into the percolation ponds of recharging the ground.(3)For other localised low lying areas, recharge pits of size of minimum 1 metre X 1 metre x 1 metre or 1 metre diameter shall be provided wherever needed, so as to prevent rainwater stagnation around the building. For other places catch water pit structures of size 30 centimetres diameter and 30 centimetres depth or higher depth, as necessary, shall be provided at the bottom of these drains at 10 to 15 metre intervals. These catch water pits shall be filled with appropriate filter materials as described in item 'B' above for ordinary building (Ground + First Floor).Explanation. - For the purposes of these rules, in regard to rainwater harvesting structures are concerned any other modifications, additional structures or alternative designs, furnished by the applicant shall be considered for approval, if it conforms to rainwater harvesting concept to the satisfaction of the competent authority for building plan approval. Provision of water harvesting structures for re-use of used water like water emanating from kitchens and bathrooms for flushing toilets, gardening shall be considered for approval on its merits.
