GO AHEAD, HIT THE
ROOF!
Simple interventions on your roof can help you harvest rain.
Here’s how
In cities, buildings are usually constructed with rooftops
of Reinforced Cement Concrete (RCC), Mangalore tiles, asbestos / galvanized
iron / zinc sheets etc. Rooftop rainwater usually flows into storm water drains
outside the plot area. As roofs are built with hard material, large quantities
of rainwater runoff and loss due to evaporation and percolation are
minimal. So, rooftop rainwater is just waiting to be harvested. You can
either store rooftop water on the roof itself, at ground level or below the
ground, using storage devices like masonry tanks, ferro cement tanks, or
plastic / metal containers.
The process
Collection: Roofs can
be broadly categorised into flat roofs and sloping roofs. Flat roofs with
RCC have water proofing on the surface as a surface finish. This surface is
provided with a slope towards the down-water pipes. For efficient
collection and effective usage, the roof needs to slope towards the storage
device. This will minimize pipe length to the storage system.
Sloping roofs with RCC, Mangalore tiles, asbestos sheets or
steel sheets lead the water to the lower edge of the roof. A gutter made out of
sheet metal or PVC has to be installed at the lower edge to collect and channel
water to the down-water pipes.
Channeling: Down-water pipes made of PVC, HDPE or cement, can be used
for transporting rainwater collected from roofs to the filtration system before
storing. The size of the down-take pipe varies depending on the roof area,
which is connected to the down pipe.
Filtration: Rainwater
collected on the roof is very pure and clean. However, there are many
substances, which may contaminate this water such as leaves, bird droppings,
dust etc. These contaminants need to be filtered before the rainwater is
stored. There are many filtration systems such as sand bed filter, PopUp
filter and stabilization tanks.
Sand bed filter:
Sand bed filter is the traditional method of filtration where coarse riverbed
sand, pebbles and aggregates are filled as layers, one above the other, in a
confined masonry structure. Rainwater is allowed at one level and filtered
water is drawn from the other.
PopUp filter: A simple
PopUp filter works effectively for residential buildings and smaller
institutional or industrial applications. It has three components – rainwater
receptor, flush valve and filter.
Stabilization tanks:
Rainwater is allowed to flow through a series of small tanks and, by providing
an entry and exit for water at strategic positions, impurities are trapped in
the stabilization tanks for subsequent cleaning.
Cost is determined by:
* Quantity of rainwater to be collected
* Type of surface from where rainwater is collected
* Existing structure and fittings for rainwater collection and flow
* Type and capacity of harvested water storage device
