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Harvesting Water at Your Home
The
rain that falls in your premises is wasted as it flows
out into the storm water drains. With the growing
demand of water for various competing uses, is it
not time for you to look at this as a Natural Resource
that can be tapped with so little effort?
Going Back
to our Traditions
Rainwater
harvesting is an ancient technique that has been practiced
in our country since ages. In a country where the
annual rainfall is concentrated for just about 100
hours a year, the only option in the absence of any
"advanced technological" means, was to conserve
and store the maximum possible portion of that rainfall.
Our ancestors realized that if they do not make every
rain drop count then they would have to spend most
of the year with a drop to drink.
Unfortunately
under the British governance system the wisdom of
the raindrop was lost. The technological interventions
which got water into our taps relied on large scale
water impoundments in the upper reaches of rivers
and pushed the wisdom of the rain drop into the background.
Today the need of the hour is to go back to the wisdom
of ancestors, rediscover their concepts and adapt
them into our lives.
The Potential
of the Rain Drop
Whether it
is a small house you are building or a country mansion
or a multistoreyed building, a simple system can help
you harness the potential of the rain drop. The rain
water harvesting systems can be incorporated in you
plans at the initial building stage itself without
much cost. With the rain water harvesting system,
you can lower your water bills, prevent local flooding
and also help recharge the declining water table.
And contrary to local beliefs, it is simple and cheap!!!
With growing
urbanziation, the percentage of hard areas in the
city is increasing. Large tracts of open land are
being brought into the urban areas for meeting the
ever increasing demand for developed land. In our
own premises itself, most of the land has been covered
with hard surfaces - the roof, the verandah, the driveway
and the portico. Consequently, most of the rain that
falls runs off the premises into the municipal storm
water that can be harvested in your premises depends
on the intensity of development and the annual rainfall
pattern in the region. On an average, through a simple
rain water harvesting system, about 40,000 litres
of rain water can be harvested from a plot of 100
sq metres in area in a region receiving 60 cm of rainfall
annually.
Benefits
of rain water harvesting
Harvesting
of the few cms of rain drops that fall within your
premises not only reduces the chances of local water
logging but also decreases your dependence on the
ground water resource. This rain water that is harvested
is pure with virtually no impurities and is suitable
for all purposes. Use of rain water for your landscaping
and green not only reduces your water bills considerably
(watering is a major component of your water consumption)
but also dissolves the soil salts and flushes them
out. As a result your landscapes become brighter and
more vibrant.
Washing and
swapping of the floors with harvested rain waters
does not even leave any salt deposits the need to
be scrubbed away now and then. After filtration the
harvested rain water can be put to all uses including
drinking and cooking purposes.
How do
you harvest the rain drop
Rain water
harvesting system can be as simple as an inverted
umbrella that collects the rain water and directs
it into a container. Alternatively, it can be a complex
system that harvests every drop of rain that falls
in your premises and then puts it back into your water
supply system. The choice of the system depends on
the size of the catchment area, the amount of rainfall
received, the end use of the harvested water and,
of course, your budget. The rain water harvesting
system can not only be incorporated in a new construction
but can also be added to any exiting structure.
Catchment
Area
The area of
your premises in which the rain water falls is the
catchment area. The nature of the catchment are a
determines the amount and the quality of the rain
water that can be harvested. The various common surfaces
have been assigned certain values of Run-off coefficients
depending on the amount of rainfall that runs off
their surface. The rainwater runs off the hard and
smooth surfaces faster than off the hard and smooth
surfaces faster than off the soft surfaces. Hence
the run-off coefficient for harder surfaces is more
than that of the soft surfaces.
The annual
rain water harvesting potential of your premises can
be calculated by multiplying the respective type of
area to the run-off factor and the amount of rainfall
that is received annually. The ideal rain water harvesting
system aims to harvest the maximum portion of this
potential and achieve "zero-run-off" in
your premises.
Collection
System
The collection
system directs the rainwater falling in your premises
into the filtration system through a system of drainage
pipes and channels. The collecting pipes collect the
rain water falling into the roof, running off the
driveway and flowing off the other open areas and
deposit into the filtration chamber. The designing
of the collecting system is done in a way so as to
collect the maximum of amount of run-off that is generated
in the premises.
Pre -Storage
/ Recharge Filtration
The rain water
dissolves the impurities that are present on the surface
as it flows through the premises into the collection
system. Therefore it is advisable to keep the catchment
area free of any chemical or other harmful impurities.
At times, it is also advised that the run-off of the
first few minutes of the rain be allowed to flow out
of the premises. This washes away most of the impurities
that may be possibly present on the surfaces. However
this calls for certain design modifications and vigilant
users. Therefore, it is always safer to make the rain
water run-off pass through a simple filtration pit
before it flows into the storage or the recharge structures.
This way, most of the impurities that get dissolved
in the rain water run-off get removed before storage
/ recharge.
Storage
/ Recharge System
Depending
on the amount of rainwater that needs to be harvested
and the proposed end use of the harvested rain waters,
an appropriate storage or recharge system is designed.
In areas with rainfall evenly spread over the year,
a simple storage cistern can be designed on the basis
of the daily water requirements. However in areas
where the rainfall is restricted to a few months of
the year, recharge systems are most appropriate. The
design and the location of these recharge systems
is site specific and needs to be evolved as per the
requirements.
Reuse system
The reuse
system depends on the need of the individual owners
and the amount of harvested rainwater that has been
passed through the simple pre-storage filtration system
can be utilized for all uses except drinking and bathing.
After adequate filtration the same water can also
be cake fit for human consumption. A harvested water
distribution system can be worked in the premises
for gardening the green areas or for use in the toilets.
Again the re-use distribution system shall be site
specific and the design shall be dictated by the site
specifications.
Maintenance
Water harvesting
systems require occasional maintenance, but this can
be easily accomplished. Debris and leaves should be
filtered before storing the water by placing screens
over gutters. Debris screens over gutters should be
cleaned periodically and storage tanks should be drained
and cleaned regularly.
Water kept
in tanks should be covered to minimize algae growth
and eliminate the potential for any mosquito breeding.
Conclusion
The
effectiveness of a rain water harvesting system lies
in its ability to meet the site specific requirements
and end use preferences. Though simple, these systems
are site specific and need to be detailed out before
implementation.
With the decreasing availability of water, rain water
harvesting presents the best option for times to come.
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