Page 174 - CW E-Magazine (28-1-2025)

Free to Die

Rainwater harvesting in cities with good rainfall

This column (to appear in the to one all. Simply write to editorial@
fourth issue of every month) is all about chemicalweekly.com. (If you would
openly sharing expertise and knowhow rather speak informally, that too can be
with our readers, regardless of industry, arranged).
product or service. The aim is plant
the seeds of inspiration, strengthen the A city like Mumbai receives on
knowledge base, and hopefully, lead to average about 2,640-mm (2.64-meters)
new opportunities and innovations. of rainfall every year. Most buildings
are ground+3 stories, though the trend
While the column is being rolled to install tall buildings is catching up
out with the ideas of Prof. V.C. Malshe, fast. Typical size of a fl at is 50-m .
2
an academician, researcher, innovator, Thus, the terrace of every fl at receives
consultant and businessman, it is open 132,000-litres of water every rainy sea-
son. If there are four residents
per fl at and there are four
fl oors, then about 8,250-litres
Rainwater
of water is available for every the highest value of the rainwater is at
resident for the four months of the highest height. Taller the building,
the rainy season. That is about more the value. Therefore, to conserve
65-litres of water per resident energy, most water should be used at
Roof Slab
per day for 120 days, enough the highest possible level without using
for his fl ushing needs. a pump, or with minimal effort. There-
fore, the idea is to construct a segmented
Most people think of harves- storage tank parallel to the height of
Top Floor
ting this water on a storage the building and collect all the water
Tank tank kept on the ground fl oor right at the ceiling level in a tank that
or an underground tank. It is would meet the needs of the residents
Flush
then required to be pumped of the top fl oor. The overfl ow of the fi rst
to the top fl oor for utilisa- tank should be collected in a tank right
tion. Since this water cannot below the fi rst tank that would provide
be treated and can be used for water to the next fl oor. The overfl ow
only fl ushing toilets, it also of the second tank should fl ow to the
requires a separate overhead third and so on. Any excess over the
storage tank and a separate full tanks may have to be drained dur-
distribution pipeline. Such a ing very high rainfall or could be stored
scheme is not implemented above ground.
due to high capital costs and
limited utility. The water is It is very easily possible to construct
free, but the cost of electri- a separate overhead tank parallel to
city to pump the water to the the building concrete or steel structure
top fl oor takes away a good with plastic tanks. The rainwater can be
amount of incentive. selectively connected to the fl ush tank
water supply as an optional source,
We need to appreciate since this is not always available right
where the value of the rain- through the year. The municipal corpo-
water is maximum. Considering rations should allow such construction
the cost of electricity at about and provide incentives to residents to
Rs.12 per kWh in Mumbai, do the same.

174 Chemical Weekly January 28, 2025

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