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.

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