Before the tank arrives
Sydney Water sets out six steps: check the regulations, check the location, find the right tank, install it, connect it, and have the plumbing inspected. The parts that matter most outside the house are these.
- Approval. Tanks that store up to 10,000 litres don’t normally need council approval, but they must meet a number of conditions; the NSW Housing Code has the current rules, and the council may have local requirements of its own.
- Inside use. To use tank water in the toilet or washing machine, Sydney Water says you must assess the site and check your backflow prevention requirements, as a property-specific backflow device may be needed.
- Ground. A full tank is heavy, so it needs a safe and stable foundation: 1,000 litres weighs 1 tonne.
- Not over the mains. Because of that weight, a tank can’t be installed over Sydney Water’s water or wastewater mains. Its enquiries line, 13 20 92, can tell you where the mains are, 8am to 5:30pm, Monday to Friday, except public holidays.
- Below ground. Underground tanks cost much more to buy and install, and need extra backflow prevention.
- The pump. Most tanks need one. An external pump usually lasts longer and stands up to more; a submersible one is thought to be quieter, and ideally have their intake raised off the bottom so they don’t draw in settled dirt.
Where price is a factor, Sydney Water suggests a tank of at least 2,000 litres connected to 75% or more of the roof, and to at least one regularly used fixture inside, such as a toilet or washing machine.
Worked example
An example only, using Sydney Water’s figure that 1,000 litres weighs 1 tonne. What a full 5,000 litre tank puts on the ground:
- Water in the tank
- 5,000 L
- Weight per 1,000 litres
- 1 tonne
- Weight of the water alone
- 5 tonnes
That is before the tank, the slab and the pump. It is why Sydney Water reminds owners to pour a concrete foundation, and keeps tanks off its mains.
Where the water goes
Sydney Water lists the plumbing connections a tank will need.
- From the downpipes to the tank.
- From the tank, when it overflows, to the stormwater system.
- From the tank to the pump.
- From the pump to the garden taps, toilets, washing machine, hot water system or other household plumbing.
The second line is the one that ties a tank to the street: the overflow goes to stormwater, never to the sewer. Sydney Water recommends a licensed plumber experienced with rainwater tanks, and an electrician may be needed too, so the pump and any auto-switching device have a safe power supply. If tank water feeds a water heater, NSW Health notes that rainwater may cause corrosion in water heating systems, and suppliers can advise on modifying them.
Clean water starts at the roof
From Sydney Water’s installation checklist:
- Skip any roof with lead-based paint or lead flashing, bitumen-based products, or exposed treated timber: rain from it shouldn’t be collected.
- Fit gutter guards or downpipe screens against leaves from overhead trees.
- Make the inlet and overflow mosquito proof, with no other way in.
- Use a first-flush device, so only the cleanest water reaches the tank.
- Fit a top-up connection or auto-switching device, so drinking water still reaches the house once the tank is empty.
Keeping it, through the year
For drinking and cooking in towns and cities, NSW Health recommends the public water supply, which is generally filtered, disinfected and fluoridated. For a tank that is used, its maintenance advice runs on a calendar.
| How often | What NSW Health suggests |
|---|---|
| Every three to four months | Clear leaves and debris from the gutters and roof, check that small animals can’t get into the tank, and cut back branches hanging over the roof. |
| Every six to twelve months | Look inside the tank for sludge and remove it, by siphoning, emptying the tank, or with professional help. |
| At least once a year | Inspect the fine insect-proof screens (for example, 1 mm) on every inlet and overflow, and make sure they are sealed and undamaged. |
| Always | Keep access covers tightly sealed against animals and children, and seal the ground-level covers of an in-ground tank so stormwater can’t get in. |
After a flood
A tank reached by floodwater is a different matter. NSW Health’s advice is that tanks affected by storms and floods are likely to contain harmful microorganisms, and the water won’t be suitable for normal use; it also shouldn’t be used if the tank or its pipework is damaged, or if floodwater has touched taps or connections inside or outside the home. Use the town supply instead.
Emptying is only recommended if the tank was inundated by floodwater, and emptying it before the ground around it has dried out may damage the tank and its plumbing. If cleaning means going inside the tank, NSW Health recommends a qualified professional tank cleaner, because of the risks of working in a confined space. The plumbing, gutters, downpipes and roof should be inspected for damage, cleaned and disinfected too.
Once the tank is refilled with clean, safe water, it can be disinfected with chlorine, and then every tap it feeds flushed for a few minutes, with screens and aerators removed and cleaned.
Worked example
An example only. NSW Health’s dose for disinfecting a tank is about 7 grams of calcium hypochlorite (powdered pool chlorine, 65% available chlorine), or 40 millilitres of sodium hypochlorite (liquid chlorine, 12.5%), for every 1,000 litres. For a full 5,000 litre tank:
- Calcium hypochlorite: 7 g × 5
- 35 g
- or sodium hypochlorite: 40 mL × 5
- 200 mL
NSW Health’s method: mix the chlorine first, outdoors, in a plastic bucket, then add it to the tank. Always add chlorine to water, never water to chlorine. Mix it through and let it stand for at least two hours. Avoid stabilised pool chlorine.
To check it worked, NSW Health looks for at least 0.5 mg/L of free chlorine half an hour after dosing, measured with a pool test kit; without a kit, a faint smell of chlorine about an hour after treatment. If you can’t smell it, a similar dose may be needed again. Ideally, leave the tank unused for at least 24 hours.
NSW Health’s full advice is on its pages about managing rainwater tanks and cleaning tanks after floods or storms; your local public health unit is on 1300 066 055.