Water Quality and Maintenance
Tank maintenance
Proper maintenance of the tank, catchment system, roof, gutters and inlet is essential to ensure a safe supply of water and is best carried out before seasons when heavy rain is expected.
Roof catchments and gutters should be inspected and cleared of leaves and other debris every three or four months. Overhanging branches should also be removed where possible. If overhead wires are too close for safety, contact your local power authority for advice.
All screens should be cleaned regularly. Tanks should not be allowed to become breeding sites for mosquitoes. If mosquitoes are detected in a tank the entry point should be located and closed. For most types of tanks mosquito breeding can be stopped by adding a teaspoon of domestic kerosene, which will eventually evaporate. Power kerosene should not be used as it will taint the water.
Desludging
Tanks should be examined for accumulation of sludge at least every 2-3 years. If sludge is present in the tank it should be removed by siphon or by complete emptying of the tank (desludging).
Do-it-yourself tank cleaning presents a number of risks including working in confined spaces. It is important to be aware of occupational health and safety guidelines.
Tanks with a ‘cone scour’ base are easy to clean by simply opening the cleaning outlet to allow the water to gush out with the sludge then rinse with a hose. Small, flat-bottomed tanks can be drained, rinsed with a hose and tilted to drain. One method of cleaning big flat-bottomed tanks is to get inside with a bucket, shovel and broom and dig out the sludge. A second person should be present to ensure the safety of the person inside the tank.
Clean a big tank early in the morning or when the area is shaded to avoid heat exhaustion. For light inside the tank, use a battery lantern not a flame or electric extension. If chemicals are being used for repairs inside, a respirator may be necessary.
Professional tank cleaners are available in some areas.
A concrete tank could crack if it dries out. Check with the tank supplier to find out if the type you have can safely remain empty for a few weeks. It might be necessary to put water in the tank to stop it from cracking.
Plastic tanks will need some water or should be tied down to stop them from blowing over in strong winds when they are emptied.
Disinfection
Rainwater can be disinfected by bringing to a rolling boil, and allowed to cool before drinking.
Regular disinfection should not be necessary (unless required on medical advice). However, if you suspect that water in the tank is contaminated, it can be chlorinated by adding powdered swimming pool chlorine (calcium hypochlorite, 65 per cent available chlorine) or liquid chlorine (sodium hypochlorite, 12.5 per cent available chlorine). You should not use stabilised chlorine (chlorine cyanurates).
It takes about 5 milligrams of chlorine per litre to disinfect your tank. This is equivalent to 7 grams of calcium hypochlorite or 40 millilitres of sodium hypochlorite per 1000 litres of water. A level dessert spoon may be used as an approximate measure for 7 grams of powdered calcium hypochlorite. A lot of the chlorine may be used up during disinfection. There should be at least 0.5 milligrams per litre free chlorine, 30 minutes after the chlorine is added – you can use a pool chlorine test kit to measure how much chlorine is in the water. Note that milligrams per litre is the same as parts per million. You should be able to smell the chlorine faintly an hour or so after treating the water. If you can’t, you may need to add a similar amount of chlorine again. Ideally the tank shouldn’t be used for at least 24 hours to allow the chlorine taste and smell to dissipate and for harmful microorganisms to be destroyed. To maintain a safe water supply after the initial dosage, 1 gram of calcium hypochlorite or 4 millilitres of sodium hypochlorite per 1000 litres should be added to the rainwater tank and allowed to stand for a minimum of two hours. The water will be safe to drink provided the chlorine smell is not too strong.
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