Rainwater Harvesting (RWH) is the act of capturing rainwater
and either storing it for use or recharging it into the ground. In Apartments,
water from clean catchments (roof) can be routed properly through suitable
conduits into a filter. Filtered water can be stored in storage structures for
subsequent use. Surface run off can be used to recharge the ground water. This
is achieved by recharge wells and/or direct tube-well recharge. The following
strategy has been found most suitable for rainwater harvesting implementation.
Storage of rainwater
for direct use: Priority is given to capture as much of the run-off
rainwater in storage such as sumps, on-ground tanks or tanks on terraces at
intermediate levels (e.g.: sit outs / balconies). However for such a strategy,
the run-off only from clean areas can be tapped. It is important that these
catchment areas be free from any form of chemical or other toxic contamination
and dust content is as low as possible. Typically roof areas qualify well for
such a strategy. The water from this run-off is first rain separated, filtered
and then let into the storage. The water can be used for all household purposes
such as bathing, washing, cleaning, gardening etc directly and can even be used
for potable purposes if subsequently it is passed through filters to deal with
bacteriological contamination (E.g.: Aquaguard filters, boiling etc).
Groundwater recharge:
Excess run-off from above mentioned clean surfaces, run-off from other
surfaces such as roads, garden area etc can then is redirected for groundwater
recharge. The most effective recharge structure has been found to be a recharge
well whose depth is a minimum of around 20 feet. These recharge wells recharge
the shallow aquifer. Water needs to be distilled adequately before allowing the
water into recharge wells. The location of the recharge wells need to be chosen
strategically – both where significant run-off water passes through the
recharge well location and which is close to existing bore wells. Recharge
wells, over time will help replenish groundwater. If the ground water table
rises above the bottom of the recharge well, the recharge well can be used as a
withdrawal well. The diagram below illustrates the principle of recharge.
Components
of Rainwater Harvesting
Conduit/ Pipes
Filtration
Storage Structures
Recharge Structures
Conduit/ Pipes:
Rainwater pipes/conduits carry water from the roof top to the ground. These
pipes have to be connected and drawn to the required location by providing
sufficient slope so that the water flows with gravity and no water is stored in
the pipes after rain stops. The pipes can also be laid underground but
sufficient care has to be taken in order to avoid damage to the pipe because of
the vehicular movement. The cost of piping depends on various factors like
quality of pipe and length of piping works to be done and many other site
conditions.
Filtration:
Rainwater has to be filtered for silt and suspended impurities before allowing
into any of the storage structures in order to store it for a longer time. Some
of the filtration methods can be implemented.
1. First rain
separator: It is a mechanism where in first few minutes of rain which
carries most of the impurities from the roof are not allowed to pass into the
filter or storage structures. It reduces the amount of silt / debris flowing
into the filter or storage structures. This in turn reduces maintenance of
filter and cleaning of the storage structure.
2. Filter:
Rainwater from the roof carries dust and suspended particles from the roof top.
These impurities have to be filtered before allowing the water for storage.
This can be achieved by passing the rain water through a chamber having layers
of graded aggregates and a layer of charcoal. The suspended particles get
trapped in the aggregate bed and charcoal adsorbs gases and odor if any. Filter
also reduces the velocity of water and hence helps in sedimentation of fine
particles in the filter.
3. Underground /
Subsurface Filters: In case it is not possible to provide filters over the
ground, underground filters can be constructed. The principle of filtration
remains the same but the filter will have 2 chambers with the filter media and
the water flows through the filter media and moves to the second chamber
through the underground pipe.
Storage Structures: Rainwater
can also be stored in HDPE tanks for secondary uses. This procedure involves
construction of a small pedestal and placing the HDPE Tank on the Pedestal and
connecting the rainwater pipe to the Tank after First rain Separation unit. The
water stored in the rain barrel can only be used for non potable purposes like
gardening, car washing etc. Proper overflow pipe should be provided in order to
avoid water logging near the rain barrel.
Recharge Structures:
Ground water can be recharged using recharge wells. Ground water recharge helps
in reviving the underground water level and can act as an additional source of
water if recharged consistently. Recharge wells are constructed by digging the
earth, placing concrete rings and packing the outer space of the ring using
boulders.
Major Advantages of
Rainwater Harvesting
A well planned RWH system can reduce up to 30% of the water
requirement from other conventional sources like bore well or municipal supply.
Rainwater Harvesting provides reliable supply of water in
rainy season.
Can be a major source of drinking water if the other
available sources of water are not fit for drinking.
Reduces the electrical power consumption as pumping water
from deeper bore wells is reduced.
Reduces the consumption of municipal water hence reduces the
stress on centralized water supply board.
Reduces chocking or flooding of the storm water drains as
most of the water is captured at the household level.
Replenishes the groundwater and secures the availability of
water for dry seasons.
Source: Commonfloor Articles
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