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Different Methods of Rain Water Harvesting

Rain Water Harvesting in Different type of Buildings:

Normally,debris, dirt and dust get deposited on the roof during non-rainy periods.When the first rains arrive, this unwanted material will be washed into the storage tank. This may cause contamination of water collected in the storage tank thereby rendering it unfit for drinking and cooking purposes. Therefore, a first flush system can be incorporated in the Roof top Rain Water Harvesting Systems (RRHS) to dispose of the first flush so that it does not enter the tank. There are two such simple systems. One is based on a simple manually operated arrangement whereby, the down pipe is moved away from the tank inlet and replaced again once the first flush water has been disposed. In another simple and semi automatic system, separate vertical pipe is fixed to the down pipe with a valve provided below the T junction. After the first rain is washed out through the first flush pipe the valve is closed to allow the water to enter the down pipe and reach the storage tank.

(1) Sloping Roofs

Roofs made of corrugated iron sheet, asbestos sheet or tiles can be utilised for harvesting the rainwater. Gutters and channels can be fixed on the edges of roof all around to collect and transport the rain water from the roof to the storage tank. Gutters can be prepared in semi-circular and rectangular shapes. Locally available material such as plain Galvanized Iron sheets can be easily folded to required shapes to prepare semi-circular and rectangular gutters. Semi-circular gutters of PVC material can be readily prepared by cutting the PVC pipes into two equal semi-circular channels. Bamboo poles can also be used for making gutters if they are locally available in sufficient quantity. Use of such locally available materials reduce the overall cost of the system.

For Thatched Roofs: Step by Step approach

  • Step 1: If the roof is thatched, polythene sheets can be used for collecting the rainwater.

  • Step 2: The collected rainwater is filtered through a filter filled with pebbles in the bottom and coarse sand on the top.

  • Step 3: The filtered water is collected either in storage tank of existing sump and the overflow water may be diverted to percolation pit nearby.

For Sloping/Tiled Roofs: Step by Step approach :

  • Step 1: In a slopped/tiled house the rainwater from the roof is collected through the gutter in the roof.

  • Step 2: The collected water is filtered through a filter filled with pebbles in the bottom and coarse sand on the top.

  • Step 3: The filtered water is collected either in a storage tank or existing sump. Over flow water may be diverted to an existing open well/bore well or percolation pit.

For common houses with RCC roof: Step by Step approach

  • Step 1: In houses with sloping roofs the rain water may be collected to the half cut PVC pipes fitted along the sloping sides and it may be directed to either sump/open well/bore well or recharge well.

  • Step 2: Check the weather the rain water drain pipes extend up to the bottom of the building.

  • Step 3: Interconnect the rainwater drainpipes if there exist more than one.

  • Step 4: To collect rainwater in a sump construct a filter champer of size 2/1/2' * 2/1/2' * 2/1/2'

  • Step 5: The bottom half of the filter chamber has to be filled either with broken bricks/bluemetal/pebbles and followed by one feet of coarse river sand. A nylon mesh has to be provided in between the two layers. The top portion of the filter chamber should be convered with RCC slab.

  • Step 6: The inlet rainwater drain pipe should be on the top of the filter chamber and the outlet pipe connecting the filter chamber to the sump should be at the bottom.

  • Step 7: Surplus spill over water from the sump may be connected with the existing open well/borewell or to the recharge well.

  • Step 8: In the absense of sump,filter champer may be connected to the existing open well/borewell.

  • Step 9: In the absense of sump,open well and bore well the rain water may be recharged through percolation pits and the bottom of bit should be in the sandy formation.

Individual houses Existing Open well

  • Rainwater from the terrace is diverted to the existing open well using PVC pipes through a filter chamber.
  • The minimum size of the filter chamber is 2.5' x 2.5' x 2.5' filled with broken bricks/ blue metal/pebbles and sand on the top.
  • The chamber may be covered with RCC slab

Existing Bore well

  • Settlement/filter tank of required size has to be provided
  • Overflow water may be diverted to a percolation pit nearby
  • The rate of recharge through bore well is less effective than open well
  • Defunct borewells may also be used.

Multi-storied complexes Percolation Pit with Bore method

  • Construct one unit for 300 sq.ft. area (approx.)
  • Construct a chamber of size 1 m x 1m x 1m
  • A bore hole is to be drilled at the bottom of the percolation pit
  • Borehole size 150 - 300mm dia with 10 - 15 ft. depth (approx.)
  • Filled with broken bricks/blue metal/pebbles
  • Suitable for clay area

Recharge well (shallow/small)

  • This is meant for large area with heavy run-off
  • Size : 3' dia with 5' - 15' depth
  • Constructed with concrete well rings
  • Side walls must be perforated
  • Bottom 1' is filled with broken bricks (for cushion)
  • Covered with RCC slab/man hole
  • Suitable for sandy sub-soil area