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Roof top rain water can be diverted to the existing
open / bore well. Along with this, rain water
available in the open spaces around the building
may be recharged into the ground through the following
simple effective methods.
Percolation pits (Small houses)
Recharge Trench (Big houses / Apartments)
Recharge wells (Large buildings / industries)
Based on the size /area of the building and the
underlying lithological nature of the formation
the said methods may be used either individually
or in combinations.
To enhance nature recharge of rain water avoid
pavements since unpaved surfaces have more percolation
rate.
Various Methods of Recharging In Individual Houses
Components of Rooftop Rainwater
Harvesting System
In domestic Rooftop Rainwater Harvesting Systems
rainwater from the house roof is collected in
a storage vessel or tank for use during the periods
of scarcity. Usually these systems are designed
to support the drinking and cooking needs of the
family at the doorstep. Such a system usually
comprises a roof, a storage tank and guttering
to transport the water from the roof to the storage
tank. In addition, a first flush system to divert
the dirty water which contains roof debris collected
on the roof during non-rainy periods and a filter
unit to remove debris and contaminants before
water enters the storage tank are also provided.
Therefore, a typical rooftop Rainwater Harvesting
System comprise of following components:
· Roof catchment
· Gutters
· Down pipe and first flush pipe
· Filter unit
· Storage tank
· Collection pit
Among the above components, storage tank is the
most expensive and critical component. The capacity
of the storage tank determines the cost of the
system and reliability of the system for assured
water supply. Following is the brief description
of each component with a study of different materials
used for each component.
Roof Catchment:
The roof of the house is used as the catchment
for collecting the rainwater. 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 as such for harvesting the rainwater.
But thatched roofs are not suitable as it gives
some colour to water and also the water carries
pieces of roof material (such as palm leaves).
Gutters:
Gutters are channels fixed to the edges of roof
all around to collect and transport the rainwater
from the roof to the storage tank. Gutters can
be prepared in semi-circular and rectangular shapes
as shown in figures. Locally available material
such as plain galvanized iron sheet can be easily
folded to required shapes to prepare semi-circular
and rectangular gutters. Semi-circular gutters
of PVC material can be readily prepared by cutting
the PVC pipes into two equal semi-circular channels.
Bamboo poles can also be used for making gutters
if they are locally available in sufficient quantity.
Use of such locally available materials reduce
the over all cost of the system.
Downpipe and First Flush Pipe:
Downpipe:
Down pipe is the pipe, which carries the rainwater
from the gutters to the storage tank. Down pipe
is joined with the gutters at one end, and the
other end is connected to the filter unit of the
storage tank as shown in figure below. PVC or
GI pipes of diameter 50 mm to 75 mm (2 inch to
3 inch) are commonly used for down-pipe. Bamboo
can also be used wherever available in suitable
size.
First Flush Pipe:
Debris, dirt and dust collect on the roofs during
non-rainy periods. When the first rains arrive,
this unwanted material will be washed into the
storage tank. This caused contamination of water
collected in the storage tank thereby rendering
it unfit for drinking and cooking purposes.
Therefore, a first flush system is incorporated
in the Rooftop Rainwater Harvesting Systems to
dispose off the 'first flush' water so that it
does not enter the tank. There are two such simple
systems. One is based on a simple manually operated
arrangement, where by, the down pipe is moved
away from the tank inlet and replaced again once
the first flush water has been disposed.
In another simple and semi-automatic system, a
separate vertical pipe is fixed to the down pipe
with a valve provided below the "T"
junction as shown in figure.
After the first rain is washed out through first
flush pipe, the valve is closed to allow the water
to enter the down pipe and reach the storage tank.
Filter Unit:
The filter unit is a container or chamber filled
with filter media such as coarse sand, charcoal,
coconut fiber, pebbles and gravels to remove the
debris and dirt from water that enters the tank.
The container is provided with a perforated bottom
to allow the passage of water. The filter unit
is placed over the storage tank. Commonly used
filters are of two types. One is a ferrocement
filter unit, which is comparatively heavy and
the other is made of either aluminium or plastic
bucket. The latter is readily available in market
and has the advantage of ease in removing, cleaning
and replacing.
Another simple way of filtering the debris and
dust particles that came from the roof along with
rainwater is to use a fine cloth as filter media.
The cloth, in 2 or 3 layers, can be tied to the
top of a bucket or vessel with perforations at
the bottom.
Storage Tank:
Storage tank is used to store the water that is
collected form the Rooftops. Common vessels used
for small scale water storage are plastic bowls,
buckets, jerry cans, clay or ceramic jars, cement
jars, old oil drums etc. For storing larger quantities
of water the system will usually require a bigger
tank with sufficient strength and durability.
There are unlimited number of options for the
construction of these tanks with respect to the
shape (cylindrical, rectangular and square), the
size (Capacity from 1,000 lt. to 15,000 lt. or
even higher) and the material of construction
(brickwork, stonework, cement bricks, ferrocement,
plain cement concrete and reinforced cement concrete).
For domestic water needs, taking the economy and
durability of tanks into consideration, ferrocement
tanks of cylindrical shape in capacities ranging
between 4,000 lt. and 15,000 lt. are most suitable.
Plain cement concrete and reinforced cement concrete
are used for tank capacities usually more than
50,000 lt. Brick, stone, cement brick may be used
for capacities ranging between 15,000 lt. to 50,000
lt.
The ferrocement tanks are usually constructed
above ground level because of the advantages,
such as, a) ease in finding structural problems/leaks,
b) easy to maintain and clean and c) easy to draw
water. It is difficult to detect the leaks and
take corrective measures in case of under ground
tanks. Water from under ground tanks cannot be
drawn by gravity. Some kind of manual or power
lifting devices need to be used for drawing the
water. Further, in coastal areas, under ground
tanks are prone to water contamination due to
fluctuation in groundwater table and leakage of
stored water.
The storage tank is provided with a cover on the
top to avoid the contamination of water from external
sources. The cover will be in dome shape having
a raise of about 20-30 cm. in the middle. The
dome is provided with two circular openings, one
for manhole and another for accommodating the
filter. A lid covers the manhole avoiding exposure
of stored water to the outside environment. The
storage tank is provided with pipe fixtures at
appropriate places to draw the water, to clean
the tank and to dispose of the excess water. They
are named tap or outlet, drainpipe and over flow
pipe respectively. PVC or GI pipes of diameter
20 mm to 25 mm (¾ inch to 1 inch) are generally
used for this purpose.
Collection Pit:
A small pit is dug in the ground, beneath the
tap of the storage tank and constructed in brick
masonry to make a chamber, so that a vessel could
be conveniently placed beneath the tap for collecting
water from the storage tank. A small hole is left
at the bottom of the chamber, to allow the excess
water to drain-out without stagnation. Size of
collection pit shall be 60 cm x 60 cm x 60 cm.
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