28
HEALTH AND SANITATION
Rainwater harvesting:
tank materials
Rainwater storage containers are available in several
materials, each with pros and cons. There is therefore a
need to weight their costs and benefits.
By Water Research Commission
In recent installations, above-ground tanks are often
plastic. Another consideration is the potential for chemicals
to leach from the tank into the stored rainwater; however,
this is primarily a concern if rainwater must be of very high
quality for one or more of the connected fixtures. In most
cases, installation and operational specifications can be
sought from manufacturers.
ABOVE-GROUND TANKS
Corrugated steel and enclosed metal
Corrugated steel tanks are often used because of their
availability, price, and aesthetic value. They can range in sizes
from a few hundred litres to tens of thousands of litres. The
large corrugated steel tanks are usually the support structure for
a vinyl bladder on the inside which actually stores the water.
Because of their size, these tanks are usually assembled
on site. An enclosed metal tank is typically prefabricated
and assembled off-site. The tank is sealed on the inside
with a potable water approved liner or sealant. They are
often more expensive than the corrugated tanks because
they need to be shipped as a whole unit.
Concrete
Concrete tanks are durable, strong, and heavy. They can
be installed above ground or below ground. There are two
common types of concrete storage containers: ferro-
concrete and monolithic-pour concrete. Ferro-concrete is a
relatively new approach where a special concrete mixture is
sprayed on and directly applied on a metal frame. This type
of approach is common in developing nations.
Monolithic-pour concrete tanks are either poured in place
or prefabricated and assembled on site. An advantage to
concrete is that they can raise the pH of the stored water.
(rainwater is naturally acidic, so it actually neutralises it).
Wooden
Although redwood tanks were once popular, they have
become more expensive and less available. If located
in a dry climate, the wood will dry and shrink, allowing
water to leak out. To prevent leaking, the tank must be
kept full, or lined.
Corrugated tank capacity can range from just a few, to thousands of litres of storage.
March 2019 Volume 25 I Number 1
The selection of one of these materials for a
rainwater storage tank will largely depend on local
availability, as well as on cost, storage requirements,
site accessibility and/or engineering specifications.
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