A community bulk buy of water tanks is now being organised in the Blue Mountains.

What you want to do with water and what you need to know?

1. Supplement town water? Do you simply want to supplement garden water, wash the dog and the car? The dog and the car don’t take much but the garden hose runs out 1000 litres per hour. That’s a lot of water. So ask yourself How long do I water and how much water do I use? Can I use grey water from the washing machine? Am I watering strategically to get the best results from the water I use?

2. Live independent of town water? Do you want to save enough water not to use the government supply? Then you will need to do a few simple calculations and know a few facts about your water usage before you order your tanks.

a. Find out: What is your average daily household use? From 50 to 500 litres What is your annual rainfall? From 500-1400 mm How much roof area do you have to catch the water? From 40 to 300 m2 What is the likely longest period without rain? From 2 to 6+ months Tanks fill up again and again, so the longest period without rain is the critical calculation for how much storage you need.

b. Calculate: Household usage per day Household usage per month (i.e. x 30 days) How much water you can possibly harvest from roofs. Remember: 1 mm of rain collected from 1 m2 surface area = 1 litre of water.

c. For example…… Your rainfall is say, 1000 mm average per year Your roof capture is 200 m2 Potential water capture if you collect all rain is: 200,000 litres You use 350 litre of water per day for the household The longest dry period is 2.5 months i.e. 75 days You need 75 x 350 litres of water i.e. 26,250 litres of water and to be sure say, 30,000 litres. If you just want to put 1000 litres per day on your garden during the dry period you still need 30,000 litres. (Remember, if you re-use grey water you will require less stored water.)

d. How many tanks? It is better not to keep all your water in one tank in case it gets contaminated or holed, so, two tanks of 15,000 litres would be ideal.

e. Where to put your tanks? On the high side of your land so you can gravity feed it to your house and garden. As windbreaks on the west or southerly sides. As heat bank for your vegetables.

f. What to do with your overflow water? Tanks fill up quickly and overflow when there are big rainstorms. So, put some in ponds, store some in the soil, compost and plants before you then redirect the water back to the environment through the usual means. Plumbers have a great little diversion gadget for this. If you are in a rural area then redirect overflow carefully through reedbeds, riffle-and-pond systems, and artificial wetlands before it enters streams and rivers. You will be astounded by the increase in biodiversity.

These need not necessarily reflect the full range of available tanks, or their shape, as they can generally be made to custom sizes. When we ask you for the size in litres, give as close an approximation as you can based on the displayed sizes.

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