Water is a renewable yet limited resource, with only 2.5% being freshwater; its use has increased significantly since 1970, leading to potential shortages by 2025. Rainwater harvesting is highlighted as a crucial technique to manage water scarcity, involving the collection and storage of rainwater from urban rooftops and surfaces. Despite its advantages, such as providing a local water supply, it has limitations like unpredictable rainfall and should not be solely relied upon for water needs.

2. Water: water is renewable resource. Three- fourth of surface is covered with
water but only a small proportion of it accounts for freshwater fit for use.
Some facts about water
Only 2.5% of the world’s water is fresh water and most of this are in the form of polar ice-
caps.
Water use as increased by 70% since 1970.
A recent report by credit issues stated that by 2025 18 will
countries experience water demand beyond supply capabilities.

3. Life is possible on earth due to the presence of water. Nearly three-fourths of
the earth's surface is covered with water. Water is also found below the earth's
surface. It is present in air in the form of water vapor. About 70 per cent of the
human body is water. The bodies of all plants and animals contain water.

4. In the past few years, there was not even enough rain. Everything had dried up
there. There was no water for drinking, for growing crops, or for animals. People
had to leave their village and go to nearby towns for some work.
During dry and hot weather periods, it is common to find dry and cracked earth
without even a single shed of water or wet areas. Lakes, rivers, and streams may as
well run dry. Well, these are the typical earth conditions that define drought.

5. Introduction:
Harvesting Rainwater for saving drinking water has gained
enormously in significance as modern water saving sanitary
technique.
This can be used for private and public buildings as well as for
many industrial areas.
Due to the storage (retention) and the usage of rainwater the water
flowing off housing estates in both reduced and delayed

6. What is Rainwater Harvesting ?
Water is our most precious natural resource and
something that most of us take for granted.
We are now increasingly becoming aware of the
importance of water to our survival and its limited supply,
especially in such a dry continent as Australia.

7. Why is it Important?
The harvesting of rainwater
simply involves the collection
of water from surfaces on
which rain falls, and
subsequently storing this
water for later use.
Normally water is collected
from the roofs of buildings
and stored in rainwater tanks.
This is very common in rural
Australia.
Water can also be collected in
dams from rain falling on the
ground and producing runoff.

8. Methods of Rainwater Harvesting
Broadly there are two ways of harvesting rainwater.
•Surface runoff harvesting
•Roof top rainwater harvesting

9. Surface runoff harvesting
In urban area rainwater flows away as surface runoff. This
runoff could be caught and used for recharging aquifers by
adopting appropriate methods.

10. Roof Top rainwater harvesting
•It is a system of catching rainwater where it falls. In rooftop
harvesting, the roof becomes the catchments, and the rainwater is
collected from the roof of the house/building. It can either be stored
in a tank or diverted to artificial recharge system.
•This method is less expensive and very effective and if
implemented properly helps in augmenting the ground water level
of the area.

11. Components of the roof top rainwater harvesting
The illustrative design of the basic components of roof top
rainwater harvesting system is given in the typical schematic
diagram.

12. Components of roof top rainwater harvesting system
•Catchment
•Transportation
•First flush
•Filter
•Storage
•Usage
•Recharge

13. Catchment
• The surface that receives rainfall directly is the catchment of
rainwater harvesting system.
•It may be terrace, courtyard, or paved or unpaved open ground.
The terrace may be flat RCC/stone roof or sloping roof.
•Therefore the catchment is the area, which actually contributes
rainwater to the harvesting system.

14. Transportation
•Rainwater from rooftop should be carried through down take
water pipes or drains to storage/harvesting system.
•Water pipes should be UV resistant (ISI HDPE/PVC pipes) of
required capacity.
•Water from sloping roofs could be caught through gutters and
down take pipe.
•At terraces, mouth of the each drain should have wire mesh to
restrict floating material.

15. Gutters
•Gutters are channels all around the edge of a sloping roof to
collect and transport rainwater to the storage tank.
•A carefully designed and constructed gutter system is essential
for any roof catchment system to operate effectively.
•When the gutters are too small considerable quantities of
runoff may be lost due to overflow during storms.
•The size of the gutter should be according to the flow during
the highest intensity rain. It is advisable to make them 10 to 15
per cent oversize.

16. First Flush
•First flush is a device used to flush off the water received in first
shower. The first shower of rains needs to be flushed-off to avoid
contaminating storable/rechargeable water by the probable
contaminants of the atmosphere and the catchment roof.

17. Filter
•There is always some skepticism regarding Roof Top Rainwater
harvesting since doubts are raised that rainwater may
contaminate groundwater.
• There is remote possibility of this fear coming true if proper
filter mechanism is not adopted.

18. Storage
Harvested rain water can be stored in sub-surface ground
water reservoir by adopting artificial recharge techniques to
meet the household needs through storage in tanks.

19. Recharge
structures Rainwater may be charged into the groundwater
aquifers through any suitable structures like dug wells, Bore
wells, recharge trenches and recharge pits.

20. Advantages of RWH
RWH systems provide water at or near the point where water is
needed or used.
 Rainwater is relatively clean and the quality is usually
acceptable for many purposes with little or even no
treatment.
 System is independent and therefore suitable for scattered
settlements.
 Local materials and craftsmanship can be used in construction
of rainwater system.
 Ease in maintenance by the owner/user
 Provides a water supply buffer for use in times of emergency or
breakdown of the public water supply systems.

21. Disadvantages of Rainwater Harvesting.
1. Unpredictable Rainfall: Rainfall is hard to predict and sometimes little or no
rainfall can limit the supply of rainwater.
2. It is not advisable to depend on rainwater alone for all your water needs in
areas where there is limited rainfall.

22. Rain water harvesting is a technique of collection and storage of rainwater into
natural reservoirs or tanks, or the infiltration of surface water into subsurface aquifers
(before it is lost as surface runoff). One method of rainwater harvesting is
rooftop harvesting

23. Water is a limited resource. What each of us does in the world, how we live, does
make a difference. As we learn the value of clean, safe water and how scarce it
truly is, we can take steps to protect it and to get it to people who lack access
today.
Did you know that nearly 1 billion people, mostly in the developing world, have
no access to safe water? More than double this number - about 2.4 billion - have
no access to any form of improved sanitation facilities. They could use your help
to get it.

24. How to save water: 10 tips for saving water around the home
The majority of household water use comes from toilets, washing machines,
showers, baths, faucets and leaks, but what you can do to save water is fairly simple.
These 10 water-saving tips will put you on the path to conserving water in your
house hold.
Turn off the tap while brushing your teeth.
Turn off the tap while washing your hands.
Fix your leaks.
Re-use your pasta cooking liquid.
Don’t run the dishwasher or washing machine until it’s full.
Flush with less.
Water outdoor plants in the early morning.
Use less electricity.
Skip the shower from time to time