Abstract :
Ground
water resource gets naturally recharged through percolation. But due to
indiscriminate development and rapid urbanization, exposed surface for soil has
been reduced drastically with resultant reduction in percolation of rainwater,
thereby depleting ground water resource. Rainwater harvesting is the process of
augmenting the natural filtration of rainwater in to the underground formation
by some artificial methods. "Conscious collection and storage of rainwater
to cater to demands of water, for drinking, domestic purpose & irrigation
is termed as Rainwater Harvesting”.
Why
rainwater harvesting?
In many
regions of the world, clean drinking water is not always available and this is
only possible with tremendous investment costs and expenditure. Rainwater is a
free source and relatively clean and with proper treatment it can be even used
as a potable water source. Rainwater harvesting saves high-quality drinking
water sources and relieves the pressure on sewers and the environment by
mitigating floods, soil erosions and replenishing groundwater levels. In
addition, rainwater harvesting reduces the potable water consumption and
consequently, the volume of generated wastewater.
Application
areas
Rainwater
harvesting systems can be installed in both new and existing buildings and
harvested rainwater used for different applications that do not require drinking
water quality such as toilet flushing, garden watering, irrigation, cleaning
and laundry washing. Harvested rainwater is also used in many parts of the
world as a drinking water source. As rainwater is very soft there is also less
consumption of washing and cleaning powder. With rainwater harvesting, the
savings in potable water could amount up to 50% of the total household
consumption.
(1) A
collection or catchment system is generally a simple structure such as roofs
and/or gutters that direct rainwater into the storage facility. Roofs are ideal
as catchment areas as they easily collect large volumes of rainwater.
The amount
and quality of rainwater collected from a catchment area depends upon the rain
intensity, roof surface area, type of roofing material and the surrounding
environment. Roofs should be constructed of chemically inert materials such as
wood, plastic, aluminium, or fibreglass. Roofing materials that are well suited
include slates, clay tiles and concrete tiles. Galvanised corrugated iron and
thatched roofs made from palm leaves are also suitable. Generally, unpainted
and uncoated surface areas are most suitable. If paint is used, it should be
non-toxic (no lead-based paints).
(2) A
conveyance system is required to transfer the rainwater from the roof catchment
area to the storage system by connecting roof drains (drain pipes) and piping
from the roof top to one or more downspouts that transport the rainwater
through a
filter system to the storage tanks. Materials suitable for the pipework include
polyethylene (PE), polypropylene (PP) or stainless steel.
Before
water is stored in a storage tank or cistern, and prior to use, it should be
filtered to remove particles and debris. The choice of the filtering system
depends on the construction conditions. Low-maintenance filters with a good
filter output and high water flow should be preferred. “First flush” systems
which filter out the first rain and diverts it away from the storage tank
should be also installed. This will remove the contaminants in rainwater which
are highest in the first rain shower.
(3) Storage
tank or cistern to store harvested rainwater for use when needed. Depending on
the space available these tanks can be constructed above grade, partly
underground, or below grade. They may be constructed as part of the building,
or may be built as a separate unit located some distance away from the
building. .
(4) Delivery
system which delivers rainwater and it usually includes a small pump, a
pressure tank and a tap, if delivery by means of simple gravity on site is not
feasible.
Disinfection of the harvested rainwater, which includes filtration
and/or ozone or UV disinfection, is necessary if rainwater is to be used as a
potable water source.Download :
rainwater harvesting report