Step by Step approach for common houses with RCC roof :

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.
Check the weather the rain water drain pipes extend up to the bottom of the building.

Interconnect the rainwater drainpipes if there exist more than one.
To collect rainwater in a sump construct a filter champer of size 2/1/2' * 2/1/2' * 2/1/2'

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.
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.

Surplus spill over water from the sump may be connected with the existing open well/borewell or to the recharge well.
In the absense of sump,filter champer may be connected to the existing open well / borewell.

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

Water Quality Monitoring
Water stored from the house roof top is presumed to be pure and potable as it will not flow on the ground and come into contact with any liquid or solid materials which can alter its quality. But, the rainwater falls on the roof, passes through the gutters and finally reaches the storage tank. In this process, water comes into contact with the dust, debris and leaf litter collected on the roof and the gutters. The water collected in the tank is stored for a period of 3 to 6 months before use. During this period, water will be in contact with tank walls and pipe fittings in the storage tank. If the stored water is exposed to outer environment it allows growth of algae and breeding of mosquitoes in the tank.
The reasons for variations in chemical constituents and bacteriological properties of water from Rooftop Rainwater Harvesting system (RRHS) could be many but the most important ones are listed below:
  1. Even though the water flows over the house roof for a short distance, it may dissolve some chemicals deposited on the roof from the atmosphere or the residue of chemical reaction between the atmospheric gases and the roof material.

  2. In general rainwater is pure and free from contamination. However, the air pollution from factories, industries, mining etc. does influence the chemical quality of water vapour in the atmosphere. When this water vapour condenses and comes in contact with the roof material, may react and leave residue on the roof. this phenomenon usually occurs over areas surrounding industries. The impact of this pollution on this rain water quality is not alarming, but needs attention.

  3. The rainwater while passing on the roof may carry the dust and debris resulting in change in the quality of water.

  4. The organic matter from the bird drops, rotten tree leaves, seeds and algae formation will be dissolved and carried by the rain water while flowing on the roof top. This may also cause quality changes of water stored in the tank.

  5. Breeding of mosquitoes or entry of insects through the opening of the tank such as over flow pipe may affect the quality of water.
The chemical and bacteriological contamination of roof water during the collection and storage processes can be prevented effectively by proper and regular maintenance of the system.

Analysis of Water samples
As the bacteriological contamination cannot be detected by the naked eye, it is necessary to analyse the quality of water in laboratories by collecting few water samples from storage tank. These tests help in verifying the presence of pathogenic bacteria. Following is the procedure for sample collection:
  • Take three clean and dry sterilized glass or plastic bottles of 100 ml. size
  • Rinse the bottles in the tank water from which samples have to be collected
  • Fill the bottles with the tank water through the tap
  • Take the water samples for testing to the nearest laboratory within 48 hours of collection of samples.
  • Observe the test reports for the presence of E-coli bacteria

    Presence of E-coli bacteria in the water samples is an indication of water contamination by pathogen bacteria, which tends to multiply. Therefore, treatment of water becomes necessary even if less number of E-coli is noticed.
Disinfecting water
Disinfecting is the process of killing the disease causing micro-organism present in the water. This can be done either by boiling the water in a vessel before consuming or by dissolving bleaching powder in required quantity to the water stored in the tank.

For disinfecting using bleaching powder, the general dosage recommended is 10 milligrams of bleaching powder containing 25% of free chlorine per litre of water. this meets the required standard of 2.5 milligrams of chlorine per litre of water.

After adding the bleaching powder, the water shall be stirred thoroughly for even distribution of the disinfectant agent. The water should be kept without use for about 30 minutes after adding bleaching powder. Following table can be referred for arriving at the quantity of bleaching powder to be added for different water depths in the storage tank.

Recommended dosage of bleaching powder for Disinfecting water
Storage
Dosage of bleaching powder ( in grams )

capacity of tank (litre)
Full tank
 Tank three fourth (3/4) full
Tank half (1/2) full
Tank one fourth (1/4) full
5,000
50
37.5
25
12.5
6,000
60
45
30
15
7,000
70
52.5
35
17.5
8,000
80
60
40
20
9,000
90
67.5
45
22.5
10,000
100
75
50
25


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