|
Sources or catchments of
harvesting Rain Water |
|
|
|
|
|
Two sources or catchments of
harvesting of rain water are there, namely
Rooftop
harvesting
and
Runoff harvesting. |
|
|
|
|
1. |
Rooftop
Harvesting |
|
|
|
|
|
In this method, catchments area
is the rooftop both in rural and urban areas.
Rooftops of houses (both in rural and urban
areas) flats, factories or office complexes (in
urban areas) which have impervious roofs are the
sources of rainwater. This is the major
component of collecting water in RWH. |
|
|
|
|
|
|
|
2. |
Runoff Harvesting |
|
|
|
|
|
Gardens, driveways, landscapes,
open fields, parks, roads and pavements and
other open areas of the environment can be used
to harvest the rain water runoff. Using this
method, it is possible to collect water from a
larger area. This is particularly advantageous
in areas of low rainfall. |
|
|
|
|
|
In a rural area this water can be
used for agricultural purposes with the collection tank made
of impermeable material. Where agriculture or gardening is
not practical in an urban area, the runoff water can be used
to recharge ground water by directing water in to a pit or
hole and allowing it to recharge ground water. The soil will
be able to filter the impurities and the water will recharge
ground water. |
|
|
|
|
|
|
|
General components of a harvesting system |
|
|
|
|
|
A typical RWH system in both
rural and urban environment has following
components, which are described below. |
|
|
|
|
1. |
Catchment
|
|
|
|
|
|
Catchment is the area
where rain water is collected. This
can be the roofs in a rooftop RWH
system and the driveway, landscape
or any other surface in a runoff
system. |
|
|
|
|
|
 |
|
 |
| |
|
|
|
Rooftop |
|
Driveway
|
|
|
|
|
|
|
|
|
2. |
Gutters and Pipes |
|
|
|
|
|
|
In a roof top system
gutters and pipes are used to
collect and transport water to the
storage tanks. These should be
properly supported and sufficiently
strong to carry and keep loaded
water during the heaviest rain.
These pipes and gutters can be made
of PVC or metal, but PVC is the
widely used.
In a runoff system
the need of gutters and pipes are a
minimum as water is collected at the
ground level. |
|
 |
| |
|
|
|
|
|
|
|
3. |
Filters |
|
|
|
|
|
Filters are used to
filter out the debris that comes
with the rooftop water and prevent
them being added to the storage
tank. There are various filter
devices,
which must be chosen according to
the purpose of using harvested rain
water. |
|
|
|
|
|
|
3.1 -
Mesh filters – a wire mesh fixed at
the mouth of or on the down pipe to
prevent leaves and debris from
entering the system |
|
 |
| |
|
|
| |
|
|
|
3.2 -
First-flushing
devices
-
first flush device is
a valve that ensures the runoff from
the earliest rains are flushed out
and does not enter the system. (The
first rains carries relatively
larger amount of pollutants and dust
from the air and catchment surface) |
|
|
| |
|
|
| |
|
|
|
3.3 - Sediment
discharge tap - this is used in the
bottom of storage tank, to flush out
the sediments settled on the bottom
of the tank. |
|
|
| |
|
|
| |
|
|
|
If water is used for
drinking purposes specially designed
filters are used. Sand filters and
charcoal filters are some examples.
Maintaining of these filters in a
good condition is essential. |
|
|
|
|
|
Gutter filter |
|
|
 |
|
|
|
|
|
Tank filter |
|
|
 |
|
|
|
|
|
|
|
|
4. |
Storage facility |
|
|
|
|
|
Storage tank
can be stationed above or under
ground. An open well can also be
used for
recharging the ground water. This storage
facility can be varied according to
the following criteria. |
|
|
|
|
|
4.1 -
Shape -
Cylindrical,
rectangular
hexangular
and square. |
|
|
|
|
|
 |
|
 |
| |
|
|
|
Cylindrical Tank |
|
Hexangular Tank |
|
|
|
|
|
|
4.2 -
Material of
construction -
Reinforced cement
concrete, (RCC), Ferro cement,
masonry, plastic (polyethylene) or
metal (galvanised iron) sheets |
|
|
|
|
|
4.3 - Position of tank -
Above ground, partly
underground, fully underground. |
|
|
|
|
|
 |
|
 |
| |
|
|
|
Above Ground Tank |
|
Partly Underground |
|
|
|
|
|
|
In a runoff system,
water can be directed to a well, pit
or trench where water is charged in
to the groundwater. Existing wells,
pits and ponds can be modified as
recharge structures. |
|
|
|
|
|
The volume of the
storage tank can be determined by
the following factors: |
|
|
|
|
|
|
1.
|
Average
annual rainfall – if the
rainfall intensity is
high, a large tank is
needed. |
| |
|
|
2. |
Period of
water scarcity – if the
rainfall pattern is
evenly distributed
throughout the year the
tank can be smaller and
if the rain is confined
to few months or weeks,
tank should be a larger
one. |
| |
|
|
3. |
Type and
size of the catchment
-
if the catchment area (eg.
rooftop) is larger, the
size of the required
tank should be larger
too. |
| |
|
|
4. |
Water
requirements – what are
the uses of harvested
water. |
| |
|
|
5. |
Number of
persons in the household
– if the number of
persons using water is
high a larger tank
should be stationed. |
|
|
|
|
|
|
|
|
5. |
Devices to Draw
water out |
|
|
|
|
|
Devices such as hand
pumps, motorised pump or tap can be
used to pump water from these
storage tanks and recharge tanks to
the points where water is used. The
device depends on the position of
the tank and the use of water. |
|
|
|
