Western Australia’s rainfall is decreasing each year. This trend started many years
and scientists predict that it will continue for many years to come.
Obtaining enough water
to meet the needs of each household will become a
problem if measures aren’t taken to
utilise all sources of freshwater.
The average home could easily harvest 100,000 L each year from their
roof. For example,
if the roof area is 200 m2 and the annual
rainfall is 900 mm, then this equates to
180 kL/yr. Obviously, it may be
impossible to collect all of the roof water, but certainly
you could catch at
Installing a rainwater tank, no matter what size, is a small step
that you could take
to improve water availability for your household needs and
for your animals. Generally,
the larger the tank the more water you can collect
and use. If you wanted to use
rainwater to flush toilets and provide water to
the laundry, then you would probably
need at least a 10,000 L tank. It is not
uncommon to install 30,000 to 50,000 L tanks
for this purpose.
- Making fresh water available to flush toilets or
to provide a laundry source.
- Using rainwater for drinking purposes.
- Supplementing the watering of garden areas.
- Reducing our use of mains (scheme) water - a
very valuable, limited resource.
- Saving some money – buying less water from a
- Providing a water source which has reduced
levels of salts and other substances.
- Providing a clean water source for stock.
Connections to the house
Rainwater is most often pumped to the house, although gravity can be
used in some cases
to direct rainwater to fixtures in the house.
Either a pressure-tank pump or a pressure-switch pump is used to
when required. When the tap is turned on, or the toilet
flushes, the pump is activated
and gently pumps water to fill the cistern, or
enter the kitchen sink or washing machine.
With the pressure-tank system, the tank on top of the pump permits
water to be
umped under pressure. Instead of the pump turning on every time
the tap is opened,
the pressure inside the cylinder may be enough to supply the
water to the house fixture.
What happens when I run
out of rainwater?
If you only install a small tank (e.g. less than 20,000 L) then it
is likely you will run out
of rainwater during the summer period. This, of
course, depends on the uses of the
rainwater. Providing a full laundry, kitchen
and bathroom service rapidly depletes the
volume you can collect during rainy
Dr Ross Mars, from Greywater Reuse Systems, installs rainwater tanks
the mains (scheme) water source with the rainwater source. He
explains that a double
check valve is connected to both, and when the rainwater
is depleted, you simply turn
a couple of ball valves to enable mains water to
enter the system. The double check valve
is the minimum requirement recommended
by the Water Corporation to prevent any
cross-contamination of mains water and
Preparation of plans to local council
Not all local government agencies require an application to install
a rainwater tank.
You will need to contact your local Council about this. Some
local government councils
also require engineered drawings from the tank
manufacturer, and these should be included
in the submission to council.
What you should also consider
rainwater tanks come supplied with a basket (leaf) filter, tap (usually brass)
and overflow pipe. Each tank manufacturer has their own fittings, but generally
filter is made from moulded plastic, the tap is either a simple
stopcock or a gate valve, and the overflow pipe is a length of PVC which
directs overflow to the ground.
steel-based tanks will also have a sacrificial anode which is buried alongside
the tank. This helps prevent corrosion of the steel body.
to these standard fittings, a number of optional extras are available for your
rainwater tank system. These include:
- Filter bag – a 20 μm cloth filter which removes most sand and dust
as the water
enters the tank.
- First-flush device. This enables the first rains to be directed away
from the tank.
This water may contain dust and decayed matter, and it is best
not to collect this
and pollute the tank water.
- Vermin proofing. This is often necessary for steel and steel-liner
tanks to prevent insects, frogs and small rodents from finding their way into
- Garden overflow. Either a subsurface piped trench or a simple
gravity-fed dripper system is installed to direct overflow more effectively to
garden areas or beds.
- Venting. Condensation is common is rainwater tanks. This is not a
problem for poly (plastic) tanks but can cause minor corrosion in steel and
A ‘whirlybird’ vent or similar is installed in the tank lid
to duct excess water vapour
to the atmosphere.
What are the costs involved?
Rainwater tanks are relatively cheap. However, small tanks are proportionally dearer, so
larger the tank the better is the cost-effectiveness. For example, a 1,000 L tank
$900, a 5,000 L tank $2500 while a 50,000 L tank is about $4500.
If you intend to pump the rainwater to flush toilets and so on, then a pump and irrigation
ilter would be about $600. Installation would be extra, and this depends on the distance
the house fixtures and the degree of difficulty in supplying water to the house.
Adding options such as a first-flush device, overflow to gardens and a filter bag could cost
an additional $400.
Remember, that if the rainwater tank is plumbed to, and supplies, the house, then a rebate
of $500 is possible from the Water Corporation. Click here to find out more about rebates.
Why should we bother?
When asked about the use of collected rainwater, installer Ross Mars, who has a
tank himself, stated “I designed my house to enable the largest rainwater
tank possible to
be positioned under the house. We have a pole home, so I ended up
with a 50,000L tank,
which has a diameter of about 6m. This volume would easily fill
several times year, and it
enables us to pump rainwater to flush both of the toilets as
well as provide a laundry source.
We live on a bush block in the hills east of Perth and
we can also use our rainwater to
protect our home from bushfire. Should the need ever
arise, we have a source of drinking
water as well.”
“I am a strong advocate for reuse schemes and I certainly have tried to convince
install either a greywater reuse system or a rainwater tank, or both.
We all know that our
rainfall is decreasing year by year and that water restrictions
are here to stay. Everyone
needs to do some future planning.”