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RAIN WATER HARVESTING
Presented by:- plumbing welfare association.
office:- Dharm plaza plot no-304/305 near R.B.L
bank n-3cidco jalna road aurangabad
Email:-pcwa@gmail.com Apsc@gmail.com
cont:-
9579555255,97303377,9022220073,9096142142
2
Rainwater harvesting (RWH): technology used for collecting
and storing rainwater for human use from rooftops, land
surfaces or rock catchments.
One of the world’s most important ancient water supply
techniques (practiced for more than 4,000 years), is beginning
to enjoy a resurgence in popularity.
Rainwater is an important water source in many areas with
significant rainfall but lacking any kind of conventional,
centralised supply system.
Introduction (1)
Why?
Economics• Reduces water bills
• Reduced water demand - water supply utility saves money on treatment and pumping
• Reduces cost of infrastructure necessary for water supply
Environment• Energy saved – no pumping of water to our homes
• If water is hard, adding soft rainwater improves water quality
• Improves groundwater situation
• Reduces demand for water at city/village level
Other• Simple, cost-effective, easy to construct and maintain
• Viable in urban and rural areas, slums, low income housing, apartments
• Can offset the need for multipurpose river projects
What is the solution ?
• Rain water is the ultimate source of fresh
water
• Potential of rain to meet water demand is
tremendous
• Rain water harvesting helps to overcome
water scarcity
• To conserve ground water the aquifers must
be recharged with rain water
• Rain water harvesting is the ultimate answer
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Use of Harvested Rainwater
Non-potable purposes (mainly in urban areas)
- Gardening
- Flushing
- Washing clothes/cars
Potable purpose after ensuring quality
(mainly in rural and peri-urban areas)
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The initial cost (mainly of storage tank) may prevent a
family from installing a RWH system.
The water availability is limited by the rainfall intensity
and available roof area.
Mineral-free rainwater has a flat taste, which may not be
liked by many.
The poorer segment of the population may not have a
roof suitable for rainwater harvesting.
Domestic RWH will always remain a supplement and not a
complete replacement for city-level piped supply or supply
from more ‘reliable’ sources.
Limitations of RWH
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Rainfall quantity (mm/year)
Rainfall pattern
Collection surface area (m2)
Runoff coefficient of collection (-)
Storage capacity (m3)
Daily consumption rate (litres/capita /day)
Number of users
Cost
Alternative water sources
Factors affecting RWH system design
Reasons of Shortage of Water• Population increase
• Industrialization
• Urbanization
• (a) Increase in per capita utilization
• (b) Less peculation area
• In places where rain fed/ irrigation based crops
are cultivated through ground water
• Decrease in surface area of Lakes, talab, tanks etc.
The typical roof top rain water
harvesting system comprises
• Roof catchment
• Gutters
• Down pipe & first flushing pipe
• Filter Unit
• Storage Tank
Roof catchment
The roof of the house is used as the catchment
for collecting rain water. The style construction
and material of the roof effect its suitability as a
catchment, Roofs made of corrugated iron sheet ,
asbestos sheet, Tiles or Concrete can be utilized
for harvesting the rain water
Gutters
Gutters are channels fixed to the edges of
roof all around to collect & transport the
rainwater from the roof. Gutters can be
made in semi-circular and rectangular
shape with cement pipe, plain galvanized
iron sheet, PVC pipes, bamboos etc. Use of
locally available material reduce the overall
cost of the system
First Flush Pipe
Debris, dust & dirt collect on the roof
during non rainy periods when the first rain
arrive. A first flush system arrangement is
made to avoid the entering unwanted
material into the Filter media & storage
tank. This is a simple manually operated
arrangement or semi-automatic system
with a valve below the ‘T’ junction
Filter Unit
The filter unit is a container or
chamber filled with filter media such as
coarse sand, charcoal, coconut fiber,
pebbles & gravels to remove the debris &
dirt from water that enters the tank. The
filter unit is placed over the storage tank or
separately. It may be of Ferro cement filter
unit, Aluminum, Cement rings or Plastic
bucket etc.
Storage Tank
It is used to store the water that is collected from the roof through filter. For small scale water storage plastic buckets, jerry cans, clay or cement jars, ceramic jars, drums may be used. For larger quantities of water, the system will require a bigger tank with cylindrical or rectangular or square in shape constructed with Ferro cement or cement rings or plain cement concrete or reinforced cement concrete or brick or stone etc. The storage tank is provided with a cover on the top to avoid the contamination of water from external sources. The storage tank is provided with pipe fixtures at appropriate places to draw the water to clean the tank & to dispose of extra water. A provision for keeping the vessel to collect the water is to be made.
Size of Storage Tank• Based on
• No. of person in the House hold
• Per capita water requirement
• No. of days for which water is required
• Example
• Drinking water requirement for a household with
5 family members, period 8 months & 6 lpcd
• = 5x 180x 6
• = 7200 Liters
Water available from Roof
Annual rainfall (in mm) x roof area (in sq. m) x co-
efficient of run off for roof
co-efficient of run off
GI sheet 0.9
Asbestos 0.8
Tiled 0.75
Plaster on bricks/ Concrete 0.7
Water available from roof top 800mmx 20
sq.m=12800 Liters per annum
Water available from Roof
continued……Size of Tank =1.2 m dia 1.8 m height
No. of Tanks 4
Volume of Tanks 3.14x1.2x1.2x1.5/4
2.03 cum
2000 liters
Volume of of 4 tanks =
4x2000
8000 Liters
(this can be designed as per requirement)
Cost of Material for Tank1. Cement 8 bags*Rs. 140.00
1120.00
2. Grit .25 Cum 200.00
3. Sand .4 Cum 100.00
4. Perforated Cement rings 5 No. 1000.00
5. P/fabricated Cement rings 4 No. 400.00
6. PVC pipe 63mm dia.*10M 200.00
7. P/fabricated Asbestos 10mm dia.*10mm
Gutters250.00
8. Mason/ Labor charges. 1000.00
9. Transportation 130.00
Total4400.00
Cost of Material for Filtration Tank
1. P/fabricated cement rings 5*Rs. 40.00200.00
2. Cement 2 bags*Rs. 140.00280.00
3. Sand 2 bags 50.00
4. Grit 4 bags 50.00
5. Charcoal 20 Kg*Rs. 8.00160.00
6. Sand for Plastering 4 bags 100.00
7. Mason/ Labor500.00
8. White washing 40.00
9. Transportation 50.00
Total1430.00
Total Cost of construction Rs. 4400.00+Rs.
1430.00= Rs. 5830.00
The cost on O/ M-
White washing 100.00
Water testing 200.00
(2 times a year)
300.00
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A solid secure cover to keep out insects, dirt and
sunshine
A coarse inlet filter to catch leaves etc.
A overflow pipe
A manhole, sump and drain for cleaning
An extraction system that does not contaminate the
water e.g. tap/pump
A soakaway to prevent split water forming puddles
near the tank.
Additionally features
- sediment trap or other foul flush mechanism
- device to inside water level in the tank
Requirements for Storage System
40
The quality of rainwater is relatively good but it is
not free from all impurities.
Analysis of stored rainwater has shown some
bacteriological contamination.
The rainwater is essentially lacking in minerals,
the presence of which is considered essential in
appropriate proportions.
Cleanliness of roof and storage tank is critical in
maintaining good quality of rainwater.
The storage tank requires cleaning and
disinfection when the tank is empty or at least
once in a year.
Quality of Rainwater (1)
41
The extraction system (e.g. taps/faucets, pumps) must
not contaminate the stored water.
The first run off from the roof should be discarded to
prevent entry of impurities from the roof.
Some devices and good practices have been suggested
to store or divert the first foul flush away from the storage
tank.
In case of difficulties in the rejection of first flow, cleaning
of the roof and gutter at the beginning of the rainy season
and their regular maintenance are very important to
ensure better quality of rainwater.
Quality of Rainwater (2)
42
The simple operation and maintenance of RWH
systems is one of the most attractive aspects of the
technology.
The extent of maintenance required by a basic
privately owned household RWH system includes
- Regular cleaning of the roof tops and gutters
- Frequent cleaning of storage tanks
- Inspection of gutters and feeder pipes and valve
chambers to detect and repair leaks
When ground catchment is used for collection and/or
ground tank is used for storage, proper fencing of both
is recommended to keep the children and animals away, thus
avoiding contamination and risks of falling into the tank.
Operation and maintenance
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