Section 3A(2)(B) in Tamil Nadu District Municipalities Building Rules, 1972
(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.