Transcript Why harvest rainwater?

Rainwater
Harvesting
What is rainwater harvesting Capturing the rainwater as it falls on
roof-tops, sides of buildings and
even concrete pavements
 Filter it
 Store it in large containers either
above ground or underground in
sumps for immediate consumption
or
 Charge the underground using
percolation pits for use during dry
months
 All forms of water found in lakes
and rivers start with the rain
 Rainwater is naturally pure.
rooftop
Covered
storage tank
Outlet tap
Cemented or treated
earth catchments
Ferro cement tank
Why harvest rainwater?
 Relief of strain on other water
supply
 Reduce water supply infrastructure
costs
Washing
 Reduced flood flows
machines
 Reduced topsoil loss
 Improved plant growth
WCs
Main water
 Improve storm water quality
supply
 Reduce storm water volume and
Gardens
peak storm water discharges
A chart showing- how simple rain harvesting
 Improve performance of Water
system can provide water for toilets, washing
Sensitive Urban Design measures machine and garden, letting us save up to half of
the mains water we currently use.
How it worksCollection of rainwater
Recharge and use
Storage
Filtration
Technical description A rainwater harvesting system consists of three
basic elements: a collection area, a conveyance
89mm
system, and storage facilities.
 The collection area in most cases is the roof of a
house or a building. A conveyance system usually
consists of gutters or pipes that deliver rainwater
falling on the rooftop to cisterns or other storage
vessels
 Both drainpipes and roof surfaces should be
constructed of chemically inert materials such as
wood, plastic, aluminum, or fiberglass, in order to
avoid adverse effects on water quality.
 The water ultimately is stored in a storage tank or
cistern, which should also be constructed of an
inert material. Reinforced concrete, fiberglass, or
stainless steel are suitable materials
140mm
125mm
Gutter
 Storage tanks may be constructed as part of the building, or may be built as
a separate unit located some distance away from the building
Roof
Gutter
Downspouts
Cover
Cistern
Roof washer (filter)
Tap
Typical rainwater catchment's system
Storage tank reservoir All rainwater tank designs should
include as a minimum requirement:
 - A solid secure cover
- A coarse inlet filter
- An overflow pipe
- A manhole, sump, and drain to
facilitate cleaning
- An extraction system that does
not contaminate the water; e.g., a
tap or pump
Types- may be underground or on
the ground
Collector device
Filter
Cleaning &
maintenance door
Underground tank
Gutter
Water collection
pipe
Tank
Water tank on the ground
Advantages Rainwater harvesting provides a source of water at the point where it is
needed.
 It provides an essential reserve in times of emergency and/or breakdown of
public water supply systems, particularly during natural disasters.
 The construction of a rooftop rainwater catchment system is simple
 The technology is flexible.
 The physical and chemical properties of rainwater may be superior to those
of groundwater or surface waters that may have been subjected to pollution,
sometimes from unknown sources.
 Running costs are low.
 Construction, operation, and maintenance are not labor-intensive.
Disadvantages The success of rainfall harvesting depends upon the frequency and amount
of rainfall; therefore, it is not a dependable water source.
 Low storage capacities will limit rainwater harvesting so that the system
may not be able to provide water in a low rainfall period. Increased storage
capacities add to construction and operating costs and may make the
technology economically unfeasible.
 Cisterns and storage tanks can be unsafe for small children if proper access,
protection is not provided.
 Rainfall harvesting systems increase construction costs and may have an
adverse effect on home ownership. Systems may add 30% to 40% to the
cost of a building.
 Rainfall harvesting systems may reduce revenues to public utilities.
Examples CITY- Chennai
 AIM- Rooftop rainwater harvesting for immediate consumption
 ANNUAL RAINFALL- 51” or 1290mm
Working Rain water collected on roof
 Flows through drain pipe
 First flush discard some initial
water
 Water flows through a filterbottom to top
 Store in a sump
 Pump the water to tank
 Store in a overhead tank- to a
house.
Designing a rainwater harvesting
system Water requirements & usage Sr. no Activities
by a family Every person needs around 135 1.
Drinking
liters of clean water per day
 These needs may range from
100 to 200 liters based on
geographical locations & life
styles.
 135 liters per day includesdrinking, cooking, washing,
bathing & gardening.
lit/person/
day
3
2.
Cooking
4
3.
Bathing
20
4.
Flushing
40
5.
6.
Washing clothes
Washing utensils
25
20
7.
Gardening
23
8.
Total
135
 Typical family of 5-annual consumption and cost Family of 5 needs 135 liters/person/day will need 2,46,375 liters in a
year.
 How much water can be harvested in a house Considering a typical house plot is about 2,400sq.ft.
 If we harvest entire 129cm of annual rainfall, it will yield 700 liters of
fresh water/ground/day.
 This will result in 2,55,500 per year.
How much a RWH unit costs Actual cost will depend upon specific RWH design, size of facility, house
and percent of rainwater harvested and stored.
 SUMP: 12,000 liter sump will cost around Rs.50,000 or about Rs.3.50 per
liter for large sumps.
 DRAIN PIPES: Rs15 to 30 per running foot
 BENDS AND ELBOWS: around rs20 to 75 per piece.
 FILTER CHAMBER OF 2’X2’X2’ WITH PEBBLES AND SAND:
Rs1,500
 10’ DEEP PERCOLATION PIT WITH SAND,PEBBLES,AIR VENT AND
A PERFORATED SLAB ON TOP: Rs2,500
 ADD LABOUR COST, SUPERVISION & TRANSPORTATION: 5%