It is not the size of the tank…

Article by Gareth Almond from Water Craft.

Rain clouds start to form on the horizon, many people will think about saving rainwater. “Is it worth it?”

Interestingly, we think of Perth as a dry city, our annual rainfall is 25% higher than London. If you had enough room for water tanks in your garden you could save enough water to last you all year, unfortunately city blocks are too small. As most people with a detached house only have space for a 2500-5000L rainwater tank, what’s the best use for that water?

Watering the garden is usually what comes to mind first. But how far will the water go in a standard 3000L slimline or ‘under eaves’ tank (typically 2500mm long and 800mm off the wall)? In the summer your official twice-weekly reticulation is designed to give your garden what Water Corp call a ‘standard drink’ – that’s 10mm per square meter, equivalent to 10mm of rain. That’s also 10 litres, so for example a 100sqm lawn will receive (100 x 10litres) twice a week, or 2000L/week. And the average domestic lawn doesn’t look great with only that amount of water. So how far will your 3000L tank go? 10 days!  Lawns and pools use a similar amount of water.

Far better to use your precious rainwater inside your home. It’s ideal for use in toilets and laundry and with a well-designed system can also be used in other parts of the home. We call this fit-for-purpose water and explicitly it means avoiding the use of expensive drinking water for purposes other than drinking. Nearly half of our drinking water comes from desalination, which is very energy-intensive. The same 3000L slimline tank fed from a single downpipe could supply all toilets and laundry in a family home from May-November each year. With two tanks you could supply the whole house for a similar period.

Whilst you’re not going to save any money, due to the current water tariff structure, you can actively help in reducing Perth’s embarrassingly high per-capita use of desalinated and ground water.

Read article ‘Perth faces a drought of action over water use‘ by Stewart Dallas for a thought-provoking background to local demands on water.