In this presentation we will learn the basics of rain water harvesting, it's components, how it works and few basic calculations associated with the sizing of components and quantity harvested

1. RAIN WATER HARVESTING
Mr. Mota Manoj H.
(Assistant professor, SITCOE)
Mr.Kate Ganesh
(Assistant professor, ADCET)

2. Rainwater harvesting is the process of collecting,
filtering and storing water from roof tops, paved and
unpaved areas for multiple uses.
The harvested water can also be used for potable
purposes after testing and treatment. The surplus
water after usage can be used for recharging ground
water aquifer through artificial recharge techniques.

3. Benefits……..
 To harness good quality water resource now
being wasted
 To prevent groundwater depletion
 To augment the expensive piped water supply
 To save expenditure on water
 To prevent soil erosion and urban flooding
 Inexpensive and simple technology
 Aids ecological conservation

4. Components of Rainwater Harvesting System:
 Catchment area
 Conveyance system
 First rain separator
 Filter unit
 Storage
 Delivery system
 Usage
 Recharge

5. How Does Rain Water Harvesting Work?
Generally rainwater is harvested from the roof of a building.
The rate at which water can be collected depends on the
plan area of the system, its efficiency and the intensity of
rainfall.
Roof catchment systems channel rainwater that falls onto a
roof into storage via a system of gutters and pipes. This in-
built collection system filters out leaves and other debris
and directs water to a vessel (an over ground or
underground tank).
From here the water is pumped to the property for non-
potable use in dry period.

7. System sizing
It is important that the system is sized to meet the water
demand throughout the dry season. Generally speaking,
the size of the storage tank should be big enough to meet
the daily water requirement throughout the dry season. In
addition, the size of the catchment area or roof should be
large enough to fill the tank.
Roof gutters should have sufficient incline to avoid standing
water. They must be strong enough, and large enough to
carry peak flows. Storage tanks should be covered to
prevent mosquito breeding and to reduce evaporation
losses, contamination and algal growth. Rainwater
harvesting systems require regular maintenance and
cleaning to keep the system hygienic.

8. Example 1:
 Calculate the amount of water that can be harvested from the
RCC building having a terrace area of 200 m2, having a garden of
20 m2 and a paved area of 50m2 around it. The average annual
rainfall is 400 mm.
Solution:
 Total water harvested= Annual rainfall X Area X coefficient of
runoff
 Coefficient of runoff for RCC building…… 0.8
 Coefficient of runoff for paved area …..0.6
 Coefficient of runoff for garden ….. 0.2
 Total water harvested= [400mm X (0.8*200+0.6*50+20*0.2) ]
= 191.6 M3
=1,91,600 lit

9. Example 2:
 Calculate the requirement of water to be harvested for a
family of 6 members. Assume the total length of dry
period to be 60 days. Assume domestic requirement to be
150 lit per person per day.
Solution:
 Requirement of water = Population X requirement per day
X total length of dry period
 Requirement of water = 6*150*60
 Requirement of water = 54000 lit