Feature

Getting Tanked

G Magazine

Rainwater is the untapped resource for many households. Here's a guide to installing your own.

Rainwater tank

Credit: Bluescope Water

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As our drinking water supplies dry up and state governments rush to spend billions on energy intensive desalination plants, we still flush our toilets and water our gardens with high quality drinking water.

Wouldn't it make more sense to reduce the pressure on our dams by installing a rainwater tank?

While generations of country Australians are accustomed to using rainwater, it's a fairly new idea for city folk.

Tank water can be used for just about everything from watering gardens and filling pools, to taking showers, washing clothes and flushing toilets.

But it seems like a great source of water that would rival the bottled variety, authorities generally discourage using it for drinking because of the potential for contamination.

Installing even a relatively small 2,250-litre tank makes a difference — RMIT researchers found if the collected water was used for the toilet and garden it could save up to 60 per cent of mains water.

How to choose a tank

These days we are spoilt for choice, with tanks available in a wide range of sizes, styles, and colours.

You can even get slim-line tanks to install along a side fence, water bladders that can be tucked under the house or a water wall that doubles as a fence.

The final choice really comes down to your budget and what space you have.

  • Plastic tanks are the cheapest but need to be located in a shady spot to prevent algae growth.
  • Concrete tanks are durable and ideal for large capacity needs, but because they're heavy structures, they'll need secure foundations.
  • Bladder tanks have the benefit of being able to collect water from all downpipes rather than just one, but they can be expensive.
  • Galvanised steel tanks cost more than plastic, but if you are concerned about embodied energy, these tanks win hands down according to researchers at the University of Newcastle.
  • How big?

    To be self-sufficient, the Australian Greenhouse Office suggests you opt for a tank between 50,000 L and 100,000 L, although few suburban backyards would be large enough to install a tank that big.

    Sydney Water advise that a 2,000-litre tank would be sufficient for toilet flushing and watering a small garden, while a 5,000-litre tank will provide enough water for clothes washing, toilet flushing and a larger garden.

    However, this is only a very rough approximation — the size of tank you will need depends on the roof collection area, total rainfall, rainfall variability, and how much water your household actually uses.

    "Choose the biggest tank that will fit on your block," advises Sydney-based rainwater tank owner John O'Byrne.

    He found that because rainfall is now so variable his tank hasn't collected as much water as he expected. Most water authorities can help you assess your needs with online calculators that use local rainfall data.

    To make maximum use of your tank connect it to the toilet and laundry.

    Unlike gardens, toilets and washing machines need water almost daily, so the tank will be emptied and refilled many times over during the year, making it more efficient.

    While it will cost more to plumb inside, rebates are often only available if you go with that option.

    Of course the tank will have minimal benefit if your household wastes water. Even the wrong toilet can make all difference!

    According to a Green Plumber calculator, a family of five with a single flush toilet will use 70,000 litres more per year than if they had a water-efficient dual-flush toilet.

    Installation requirements

    Since water is heavy, most tanks will need a secure base to prevent them from falling over.

    If you are going to use a pump, consider a submersible pump to minimise the noise. A pump may not be needed if you can install the tank at a high point or on a stand — although check to see if gravity feed will provide sufficient pressure.

    An overflow device is essential because it prevents flooding during a downpour by redirecting excess rain to the stormwater drain.

    A backflow prevention device might also be needed."They are often required for below-ground tanks where there is a greater risk of contamination with mains water," says Gary Workman, national training manager for Green Plumbers.

    You also need to decide how to maintain a mains water connection.

    If your tank has a top-up system it will automatically refill with mains water when it reaches a certain level.

    "The advantage is it only costs $250, although you cannot use the tank water on your garden when there are water restrictions," Workman says.

    "An interconnection device, on the other hand, guarantees your internal plumbing always has access to mains, but at around $1,000 it is expensive."

    Health and safety

    While rainwater is generally pretty clean, there are a few precautions you need to take, especially if you want water for inside use.

    1. Check if your roof is suitable for collecting rainwater
    2. Avoid asbestos cement roofs and those painted with lead or bitumen-based paints.
    3. If you are collecting drinking water is also important to remove any lead flashing.
      Since rainwater can pick up pollutants from dust, dead animals, and droppings, install a first-flush device on each down pipe to ensure the first few polluted litres are redirected into the stormwater drain.
    4. Insect screens to keep out mosquitoes are another must, and need to be cleaned out regularly, as do the gutters.
    5. Every three-or-so years check to see if you need to clean the sludge out of the bottom of the tank.
      If you don't want to clean it yourself you can always hire a professional tank cleaner to do the dirty work.
    How much will it cost?

    It's difficult to generalise costs because it depends on so many variables. A basic 2,000-litre plastic tank, including a first-flush device and plumbing costs will set you back about $2,000 - $2,500, says Workman.

    If you include a rebate of, say, $1,150 it will bring the cost down to between $850 - $1,350, he adds.

    Installing your tank

    "Find a plumber who has done it before," says John O'Byrne. "Otherwise you might find you need to step them through it." Workman agrees, and recommends choosing a Green Plumber who has been trained in how to install rainwater tanks.

    Regulations vary widely so don't forget to check with your local council and water authority before you purchase your tank.

    Rebates are usually collected once the tank is installed, but check first to see that your installation will meet requirements.