Bangalore Environment Trust Newsletter, August
Sat, 03/03/2007 - 19:59 — admin
Provision of adequate and safe drinking water is the prime concern
of any community. This has been achieved in most of the water
scarce villages through tapping of ground sources. Excess tapping,
high mineral concentration and pollution of even this water has
resulted in it becoming scanty and unsafe.
Women report problems of salinity, excessive consumption of fuel
in the cooking of dha1, wastage of soap in laundering and
splitting of milk while boiling with this water. Many of them
reported walking 1 to 2 kms for fetching potable water for their
One of the viable technologies for tiding over such a crisis is
harvesting of rain water from the roof surfaces of houses and
Rain water collected from roof surfaces during the first rain will
be dirty and contaminated with dust, birds droppings and other
impurities on the roof surfaces. It would, therefore, be advisable
to discard the first sweep off called `foul flush' and collect
only the remaining flow for' consumption after proper
Parameters influencing storage capacity
It is advisable to study the rainfall rate of the area for a
period of 3 to 5 years from the available records in order to
assess the economic viability of this technology.
Construction and Process
A rain water harvesting unit comprises of the following:
Down-take pipe (conduit)
Foul flush seperator
A roof of any shape forms the catchment area for this water
The rain pouring on the roof is collected in valley gutters fitted
to the caves. Gutters made of asbestos-cement or galvanized iron
are suggested for a sloped roofing. This is fixed in such a way as
to allow a free flow of water to the side, where it is provided
with a downtake pipe.
An AC pipe or PVC pipe of 10 cm (4 inches) diameter connected to
the gutters, directs the water to the foul flush separator.
This is an interception mechanism provided with arrangements for
discarding the flow of water from the roof surface whenever it is
not needed and its diversion to the storage tank whenever desired.
Designs that require different types of operation have been
In figure I, a flexible tube (No.3) connected to the downtake pipe
or conduit (No.2) leading to an interception tank (No.4), which is
a small surface tank, serves the function. During initial rains,
the tube is left outside the tank. When clear water starts
flowing, water is collected by introducing the flexible tube
(No.3) inside the tank. ,~.s this tank gets filled up, the surplus
overflow moves constantly to the bigger storage tank or well.
In figure III, the down take pipe (1) allows the water to run into
the base of a chamber filled with graded *stones (2). The plug (3)
provided at the bottom of this chamber is kept open to discard the
initial flow from the roof. Once clean water starts flowing, the
plug is closed to permit the surface flow from this unit to move
to the storage tank (4) after passing it through the filter media
The automatic foul-flush separator (3) is shown in figure N. It is
a tank with conical shaped top with a mouth and an air vent pipe
(1), a float valve (2), a tap (4) at the bottom and a lead to the
storage tank (6) The capacity of the tank is worked out at the
rate of 5 litres/sq.m roof area, the quantity assumed for cleaning
the roof area.
The down-take pipe is connected to the mouth of this tank. As
water flows into the tank, the float (2) rises up and finally
blocks the passage, directing further flow to the storage tank
(6). This tank needs to be emptied after every monsoon to prevent
chances of dirty water flowing into the collection tank, during
subsequent seasonal rains.
This can be a surface tank or a sub-surface tank.
Its size is to be estimated from the parameters prescribed.
The surface tank occupies space but can facilitate safe and easy
The sub-surface tank does not occupy any surface space. It is to
be covered and provided with a hand pump for facilitating safe
Dried up wells can also be cleaned and used as storage tanks. This
has the duel advantage of charging the ground water sources with
pure water and solving the problem of water shortage.
It is becoming an urgent need of the day to popularise the
non-conventional rain water harvesting techniques in problem areas
for augmenting diminishing drinking water sources. Wherever ground
water contains a high precentage of mineral salts, this technology
is viable for providing soft water.
Chlorination is needed immediately after the first rain and after
the last rain. It is desirable to chlorinate the stock of water
once in three months, after confirming its chlorine demand.
It varies according to the design, the area and the materials
used for installation
Dr. N. Kamalamma
Shri. E.K.N. Varma Raja
Gandhigram Rural Institute, Gandhigram
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