Siting a tank
Where tanks can go
Where you intend to place your tanks will largely influence their size and shape and possibly even their colour if they need to blend with the surrounding vegetation or dwelling. If you do not have access or the space for large tanks, use two or more smaller tanks to get the same storage capacity. Tanks can be interconnected even when they are not next to each other, so they don’t all need to be in the same location.
Most tanks will survive longer if not kept in direct sunlight. Keeping leaves away will also help tanks with flat lids stay clean.
In most cases poly tanks can be placed on a sand base, pavers or even partly into the ground. Metal tanks, however, need to be installed on a concrete base or reinforced pavers. Some large metal tanks can be assembled on site, potentially resolving access issues that prevent installation of other large tanks. Concrete tanks can be prefabricated or constructed on site.
Don’t forget about the spaces under the house or under decking which may be suitable for rainwater storage. Water storage tanks can even be placed within concrete slabs during building construction.
Underground tanks involve excavation and are generally more expensive than above-ground tanks but can be the best option for some sites with smaller yards or where large volumes of water are required. Once a tank is installed, the space above can be landscaped or paved for other uses. If you live in a bushfire- prone area, underground tanks may be your best option. Above-ground poly tanks can melt down to the waterline if a bushfire gets too close and in severe fires even above-ground metal and concrete tanks can become unusable.
Wet systems/dry systems
The terms "wet" and "dry" refer to the type of downpipe system between the roof collection area and the tank(s). In a dry system, water flows downwards from the gutter through a sloping pipe into the top of the tank. When the rain stops, the pipe empties into the tank and becomes "dry", that is, there is no residual water in the pipe. Dry systems work where the tank is close to the house and on the same side of the house as the downpipes, or when tanks are placed underground.
With a wet system, part of the pipework between the tank and the guttering is lower than the top of the tank, and is usually buried in the ground. This may be required for various reasons, such as the tank and gutters being on opposite sides of a house, requiring the pipework to run under the house to reach the tank. Other obstructions such as a driveway can be a reason for this set- up. When the tank is a long way from the home, a wet system is often used to get the pipes out of the way and eliminate the need for pipe supports, as would be required if the pipes were suspended above ground.
While it is important to ensure that all your piping is adequately insect-proofed, it is particularly important in wet systems to prevent mosquitoes and similar bugs breeding in the wet pipes. A wet system also requires an access cap at the lowest point to allow stagnant water to be periodically flushed out.
Plumbing guidelines and regulations
State and local government planning and building regulations need to be taken into account before installing a rainwater tank. Rainwater systems also need to be installed in line with the relevant plumbing regulations and standards. According to plumbing regulations, the connection of the rainwater tank to the guttering and the overflow connection to stormwater need to be done by a licensed plumber. Plumbing of the rainwater to the house also needs to be consistent with the plumbing code and Australian standards, with connections made by a licensed plumber.
Backflow prevention is required where rainwater is connected to the household water supply. Australian standards specify that the water supply from a rainwater tank needs to be clearly marked with the word “rainwater” at least every half a metre. Green plastic pressure pipe designed to meet this standard is on the market. As well, the taps or outlets using the rainwater supply are required to be labeled with the world 'rainwater' or with the letters "RW" in green.
For more information on regulations in your state, please click here.
Where should the tank be connected?
The tank can be connected to feed a garden, toilet, laundry and hot water system or even provide drinking water for a whole house. If the water is to be used for drinking and food preparation it should comply with the Australian Drinking Water Guidelines. The decision to use rainwater for drinking and food preparation in an area where there is mains water is taken at the risk and responsibility of the property owner. For non-mains areas where rainwater is the only source of water, it may be used for all plumbing fixtures and hose taps in accordance with local Health Department guidelines.
Our advice is that you use the Tankulator to help you determine where to plumb your tank water.
What size tank should I get?
Access and space for tanks will be limiting factors, but the ideal size will balance what you want to use the water for, the number of people in the household, your budget, roof size and rainfall. For example in Melbourne (annual rainfall about 650mm), a typical suburban house with a garden will need tank capacity of about 20,000L to supply the whole property. However, tanks just for the toilet or laundry can be much smaller than tanks for the garden. That is because gardens generally need large volumes of water at once, rather than small amounts regularly.
Our advice is that you use the Tankulator to calculate the right tank size for your home based on your consumption and local rainfall data.
A rainwater tank should never be situated near gutters under a large tree. It is almost impossible to keep the debris from the tree from contaminating the water.
I would have liked advice on the appropriateness of the location of the tanks because we are on a very steep hill and the house and tanks are situated low on the hill. I would have preferred to have known about the problems in moving water up the hill so I had sufficient head to water the garden at the top of the hill. As it is, I don't use the water in the tanks as effectively as I could.