Rain Water Harvesting
Rain water harvesting in a building site includes storage or recharging into ground of rain water falling on the terrace or on any paved or unpaved surface within the building site.
1 The following systems may be adopted for harvesting the rain water drawn from terrace and the paved surface.
i) Open well of a minimum of 1.00 metre dia and 6 metre in depth into which rain water may be chanelled and allowed after filtration for removing silt and floating material. The well shall be provided with ventilating covers. The water from the open well may be used for non potable domestic purposes such as washing, flushing and for watering the garden etc.
ii) Rain water harvesting for recharge of ground water may be done through a borewell around which a pit of one metre width may be excavated upto a depth of at least 3.00 metres and refilled with stone aggregate and sand. The filtered rain water may be channeled to the refilled pit for recharging the borewell.
iii) An impervious storage tank of required capacity may be constructed in the setback or other than space and the rain water may be channelled to the storage tank. The storage tank may be raised to a convenient height above the surface and shall always be provided with ventilating the surface and shall always be provided with ventilating covers and shall have draw-off taps suitably placed so that the rain water may be drawn off for domestic, washing, gardening and such other purposes. The storage tanks shall be provided with an overflow.
iv) The surplus rain water after storage may be recharged into ground through percolation pits or trenches or combination of pits and trenches. Depending on the geomorphological and topographical condition, the pits may be of the size of 1.20 m width x 1.20 m length x 2.00 m to 2.50 metre depth. The trenches can be or 0.60 m. width x 2.00 to 6.00 metre length x 1.50 to 2.00 mtr depth. Terrace water shall be channelled to pits or trenches. Such pits or trenches shall be backfilled with filter media comprising the following materials.
a) 40 mm stone aggregate as bottom layer upto 50% of the depth;
b) 20 mm stone aggregate as lower middle layer upto 20% of the depth;
c) Coarse sand as upper middle layer upto 20% of the depth;
d) A thin layer of fine sand as top layer;
e) Top 10% of the pits/trenches will be empty and a splash is to be provided in this portion in such a way that roof top water falls on the splash pad.
f) Brick masonry wall is to be constructed on the exposed surface of pits/trenches and the cement mortar plastered.
The depth of wall below ground shall be such that the wall prevents lose soil entering into pits/trenches. The projection of the wall above ground shall atleast be 15 cms;
g) Perforated concrete slabs shall be provided on the pits/trenches.
v) If the open space surrounding the building is not paved, the top layer upto a sufficient depth shall be removed and refilled with course sand to allow percolation of rain water into ground.
The terrace shall be connected to the open well/borewell/storage tank/recharge pit/trench by means of H.D.P.E./P.V.C. pipes through filter media. A valve system shall be provided to enable the first washings from roof or terrace catchment, as they would contain undesirable dirt. The mouths of all pipes and opening shall be covered with mosquito (insect) proof wire net. For the efficient discharge of rain water, there shall be at least two rain water pipes of 100 mm dia mtr for a roof area of 100 sq mtrs.
3 Rain water harvesting structures shall be sited as not to endanger the stability of building or earthwork. The structures shall be designed such that no dampness is caused in any part of the walls or foundation of the building or those of an adjacent building.