The need of the hour -- Water
Conservation and Rainwater Harvesting
by Shanaz Ramzi
After seeing the havoc wreaked by the recent
rains in Lahore and keeping in mind that there is no effective drainage system
in Karachi, one can only cringe at the thought of what lies in store for this beleaguered
city once the predicted rainfall hits the metropolis this month, or thereabouts.
Together with the devastation it will cause, is the glaring realization that as
a nation we are complicit in criminally wasting water when there is not enough
even for consumption. According to a report by United Nations Development
Programme, in another seven years Pakistan is likely to run dry. How can we
live with such apathy in the face of this terrifying knowledge? It is time we
collectively did something to change the situation and our future, instead of
waiting for the government to bail us out (excuse the pun) of our predicament.
Since there is little doubt that the issue
of water scarcity needs to be dealt with on war footing, as also rightly
emphasised recently by the Chief Justice of Pakistan, there are several aspects
that need immediate consideration. While large storage capacity in the form of
dams and barrages is essential, both to harness rain water effectively, and to avoid
devastation from flooding, it in any case needs to be dealt with in
coordination with conservation in the usage of water, replenishment of
aquifers, and rain water harvesting (RWH), since water is in any case in short
supply. Considering that water demand is constantly on the rise owing to exponential
population increase, there is constant degradation of water quality, rise in
cost of supply and maintenance infrastructure, and minimal ground water
recharging with depletion of water levels, it is shocking that no step has been
taken to date to at least harvest rain water.
If collectively, we make a conscious decision
this time round, though, to do rain water harvesting if nothing else, we could
easily minimise our losses – by avoiding the havoc of flash flooding -- and use
the impending rainfall to our advantage, both in the suburbs and in the main
city where rain run-off could be used for plantation and soil regeneration,
among other things. Even with low rainfall, rain water harvesting can lead to saving
substantial quantities that can be used for drinking as well as for non-potable
use such as domestic, indoor plantation and agriculture and also aquifer
replenishment. Studies show that 30-45 per cent of water usage is for washing,
gardening, vehicle washing and in affluent areas up to 20 per cent is used for
flushing WCs, and this usage can easily be met through RWH.
To deal with water scarcity, in many
countries it is mandatory to collect rainwater, especially in all new
developments. For example, in Central American countries storage tanks have to
be provided to store minimum 400 l of rainwater per square metre of roof area. In
Pakistan, as indeed in other parts of the world, RWH can be taken up through
either storing water from building roofs, or diverting rain water in order to
avoid flash floods.
How
can rain water be stored?
Directing water from roofs into tanks or
cisterns could provide substantial quantity of water for non-potable use as
well as cause reduction in roof runoffs thus mitigating the quantum of flash
floods. If precautions are taken and water is treated it can also be used for
drinking, thus lowering the stress on piped water supply.
All that needs to be done is to connect the
drainage pipe from the roof to a drum below – if the pipe drains out into a
cemented portion of the house – where the water can collect. The drum, in turn
should have a pipe connected to it that drains the collected water into an
aquifer pit dug in the garden or if there is no garden, then into a tank made
for the purpose in a concrete portion of the house, or directly into a pit, if
it drains into the garden.
How to make an aquifer pit:
According to retired architect and conservationist, Yasmeen Lari, aquifer
pits 1 to 2m wide, 2-3 m depth are sufficient to meet storage requirements of
houses with 100 sq m roof. To store potable water, the base should have a layer
of boulders 5-20 cm in size, gravel 5-10 mm, and coarse sand on top 1.5-2mm
graded. This will allow filtration of rainwater. For smaller roofs, the pits could
be filled with brick bats. Fine mesh should be placed on top to avoid leaves,
insects, sand and other impurities from falling in.
If the tank is being used to store water for
domestic consumption, a tap could be installed, and the water could be used
directly to water the garden or for washing cars. For other domestic use, such
as for flush systems, a separate pipe would have to be installed. In cases
where houses or even buildings are still under construction it is imperative
that these tanks be created from the very beginning and are part of the floor
plan, as they are the need of the hour.
Storing rain water serves a dual purpose, as
mentioned earlier, for aside from conservation it also helps prevent flash
floods. As the urban areas get more and more built up, in addition to the run
off from roofs, the runoffs from pavements and hard surfaces keeps increasing. Our
storm water system has proved dismally inadequate in most of our cities, and
the Karachi nullahs, once built to carry rain water are either blocked, built
upon, or full of trash. Even if they could be cleared they would hardly be able
to carry the enormous quantity of water flowing from roofs, pavements and other
hard surfaces. The destruction caused by these flash floods affects stability
of structures and grinds life to a halt, as witnessed most recently in Lahore,
and what’s more, poses a threat to human life.
Hence, the run off from pavements must be
harvested as well. In order to avoid flooding, street water must not be allowed
to enter the drainage system. Instead, catchment areas should be created so
that rather than have the water drain off from one’s property on to the
streets, and eventually into drains, or be pumped out, as is usually the case,
it works the other way around, and the water is trapped in collection devices
such as storage tanks, deep V-shaped trenches, disused pits and tube wells. Lari
recommends that the trench should ideally be 1m wide, 1.5 m deep and 10-15 m
long for roof area
200 sq m. Of course, all these containers should be covered to avoid
contamination from human, animal and other environmental pollutants, not to
mention for safety reasons.
In order to take this up on war footing, not
only individual homes but multi-storey buildings, government offices and residential buildings, courts,
stadiums, parks and hotels should all get involved. The government needs to identify and mark on maps open spaces, parks and
green areas where pits/tanks could be dug; lowest point where water collects in
each area and its disposal in trenches tube wells, old tanks, pits, etc.
Slits should be made in curbs to direct street
water into landscaped areas, while ponds could be created to serve as
wetlands in parks. It must be made mandatory for hotels and residential and
office buildings to build rain-water storage tanks for their own use. Similarly, it must be made mandatory for new developments to be
equipped with RWH mechanisms, particularly storage tanks, to relieve the stress
on piped water supply systems.
Together we can make a difference. There are
many other ways of conserving water too, but that would call for a separate
article. At the moment, if we just concentrate on rain-water harvesting, which
is the need of the hour, we could perhaps save ourselves from the predicament
we always find ourselves in during the monsoon season, and even turn it to our
advantage.
