Courtesy of CHOICE
Outdoor use
Using collected rainwater for outdoor purposes only is easiest. Apart from the obligatory checks with your council and water supplier, you just need the supplier to install the tank and don't need a licensed plumber if there's no connection to the mains water supply. Your water savings won't be huge, but you will save on the water you used to pay for to water the garden, wash the car or top up the pool.
Indoor use
Using the rainwater for toilet-flushing, the washing machine or any other indoor use will increase your water savings substantially. But to do this you need a licensed plumber to connect the tank to your mains water supply (so you can still wash a load, etc, if the tank is empty) and the approval of the relevant authorities.
If you're allowed to connect your tank to the mains water supply, you're likely to need a backflow prevention device so your rainwater won't contaminate the mains supply if the water pressure changes suddenly and the water tries to flow backwards. Your water supplier may provide this free.
Drinking water
Many water suppliers and health authorities in Australia recommend that you don't drink the water you've collected in a rainwater tank if you have access to mains water. This is probably just to be on the safe side, because no authority can guarantee the quality of the rainwater you collect. You'll also be missing out on the benefits of fluoridated water if it's supplied in your area.
Reports of illness associated with rainwater tanks are relatively infrequent and public health studies in South Australia (the state with the highest rainwater usage rate) have also failed to identify a link. So it's up to you.
Rainwater is generally regarded as fit to drink if it smells, tastes and looks fine. In areas with heavy industry, smelters or heavy traffic, atmospheric pollutants could pose a problem, as could potential pollutants on your roof, such as chemicals from paint, bird droppings, dust and leaves.
Your roof
Roofs made of galvanised iron, Colorbond, Zincalume, slate and clay/ceramic or concrete tiles are okay for collection of drinking water.
Lead-based paint (if your roof was painted before 1970) and tar-based (bitumen) coatings should be avoided. If your roof was painted with acrylic paint, avoid the first few runoffs, which can contain dissolved detergents and other chemicals.
Make sure there's no chemically treated timber or lead flashing in roof catchments and water shouldn't be collected from parts of the roof where there are flues from wood burners.
While asbestos fibres are dangerous when inhaled, it's believed asbestos roofing sheets pose no risks for water collection, as long as the material is left undisturbed.
