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1.Rain water Harvesting :
Rain water harvesting is the accumulating and
storing of rain water for it reachen the aquifer.
It has been used to provide drinking water, water
for livestock, water for irrigation, as well as other
It can supplement the subsoil water level and
increase urban greenery.
Water collected from the ground, sometimes from
areas that are especially prepared for this purpose,
is called stormwater harvesting.
Benefits of Rain Water Harvesting;
1. Availability of water for drinking, water for live
stock,water for irrigation etc.
2. Recharge of ground water table.
3. Increase in greenery in urban areas
4. system can be simple to construct from
inexpensive local materials.
5. It is environment friendly.
6. Prevents soil erosion and flooding in urban areas.
7. Inculcates a culture of water conservation in the
8. Community water resources act as social
Roof top rain water harvesting System :
Roof top rain water harvesting or domestic rainwater
harvesting is the technique through which rain water is
captured from roof components and stored in
tanks/reservoirs/ground water aquifers.
It consists of conservation of roof top rain water in
urban areas and utilizing it to augment ground water
storage by artificial recharge.
This technique is particularly useful in dryland, hilly,
urban and coastal areas. If the system is properly
installed and maintained, clean water fit for drinking
can be collected and stored
Components of roof top
rain water harvesting system
The various components of roof top rain
water harvesting system are
1. Roof/ catchment area
2. Gutters and downpipes
3. Filter unit or leaf screen
4. Storage tank
5. Delivery system
6. Water treatment unit
1. Roof/catchment area:
The terrace of a building act as a
catchment area for collecting water in
A flat roof is usually made of RCC.
If tiles are fixed on the top of the
roof,good quality of water can be
2.Gutters and Downpipes
Water from roof/ catchment area is
collected into gutters.
Commonly two types of gutters are used
1. Eaves gutter
2. Box gutter
3.Filter unit or Leaf screen
The rain water collected from the roof
should be allowed to reach the storage
tank only through a filter unit.
Rubble, sand and charcoal, as used the
traditional three-pot filtration, can be
Water from filter unit is stored in the storage
tank. Mainly three types of storage tanks are
constructed for roof water harvesting.
They are as ;
1. under ground,
2. on the ground
3. above ground tanks.
The under ground tanks are usually made of
masonry or Rcc. The overhead tanks are made
of PVC or masonry
5.Delivery system :
The water from the storage tank is
delivered to the treatment unit through
delivery pipe system.
6. Water treatment unit :
The water stored in the storage tank should be
treated if it is to be used for drinking.
Normally, filtration, sedimentation, disinfection,
etc. processes are followed for the treatment of
design of storage :
The design of storage tank depends upon
(i) Average annual rainfall
(ii) Size of catchment
(iii) Drinking water requirements
Example: Design a storage tank for drinking water
for the following data :
Number of members in the family = 5
Roof top area = 100 m
Average annual rainfall = 600 mm
Runoff = 0.85
coeficient coefficient for evaporation,
Spillage and first flush, etc. = 0.80
Daily drinking& cooking requirement =
= (area of roof top )x (annual rainfall(in m)) x
(Run off coefficient) x (Coefficient for
evaporation first flush etc.)
= 100 x 0.60 x 0.85 x 0.80
= 40.8 m3
= 40,800 litres
The tank capacity has to be designed for dry
period i.e. the period two consecutive rainy
seasons. With monsoon extending over 4
months, the dry season is of 245 days is
Drinking water requirement for
family for dry season:
= 245 x 5 x 10
= 12,250 litres
As a safety factor, the tank should be
built 20% larger than required.
quantity of water to be stored in the tank
= 1.2 x 12,250
= 14,700 litres
= 14.70 m3
Size of rectangular tank:
Size of rectangular tank =
= 3.5 m x 2.5 m x 1.7 m
= 14.875 m3
Recharge Structures :
The water conected from roof tops of large
buildings can be used for artificial recharge of
The various type of recharge structures are
1. Recharge through abandoned Dug well
2. Recharge through hand pump
3. Recharge pit
4. Recharge Through Trench
5. Gravity Head Recharge Tube well
6. Recharge Shaft
• References ;
1. U.R.patel,V.A. patel,M. Balya and H.M.
Rajgor.Roof top rain water harvesting
(RRWH) at SPSV campus Visnagar :
gujarat – A Case study, international
journal of research In engineering and
2. S.D. Khandagale & V.A. Joshi Rain water
harvesting: grab hold of water where