Microbiological and chemical hazards in rainwater
The types of microbiological and chemical hazards found in rainwater, irrespective of domestic, community-based of commercial use
Rainwater collected from a roof is generally safe to drink but collecting a good, clean supply depends on "low maintenance - not no maintenance".
Rainwater can provide a free and renewable supply of soft, clear and odourless water for a range of purposes including drinking, food preparation, washing, bathing, laundry, toilet flushing and gardening.
Generally rainwater is safe to drink.
If the rainwater is clear, has little taste or smell and is from a well-maintained system, it is probably safe and unlikely to cause any illness for most users.
Disinfecting the water before consumption should be considered for those who are immuno-compromised such as the very young or very old, cancer patients, people with diabetes, organ transplant recipients or people who are HIV positive. This can be achieved by bringing the rainwater to the boil. Alternatively, for continuous disinfection a UV light can be installed.
Rainwater collected in tanks generally contains few chemicals. However, there may be increased pollution by airborne contaminants from very heavy traffic or in industrial areas.
Collection of rainwater for human consumption (drinking and cooking) in areas affected by very heavy traffic, industry, incinerators and smelters is not recommended.
The microbiological quality of rainwater collected in domestic tanks may not be as good as mains water, but if collection systems are well maintained, the risk of harmful organisms being present is low.
See the Microbiological and chemical hazards in rainwater page for further information on microbial and chemical hazards in rainwater.
Rainwater does not contain fluoride. Where rainwater is the major source of water for drinking and cooking, advice about alternative sources of fluoride should be sought from your local dentist, school or community dental service or from the Australian Dental Association.
The supply of good quality water depends on ensuring correct design and installation followed by sensible maintenance of the rainwater tank and catchment area. The collection of rainwater involves "low maintenance — not no maintenance".
Tanks are available in a wide range of materials including galvanized, AquaplateTM or zincalume® steel, concrete, fibreglass or plastic. All these tank materials can be suitable if the tanks have been manufactured specifically for the collection of rainwater.
Some new tanks may need to be washed or flushed before use. The manufacturer should be able to provide advice on whether this may be necessary.
When installed, the tank should be covered and all access points (except the inlet and overflow) should be sealed. The inlet should incorporate a mesh cover and a strainer to keep out debris and prevent the entry of mosquitoes and other insects. The overflow should also be covered with an insect-proof screen.
In general, house and shed roofs are used as catchment areas. Rainwater can be collected from most types of roof, including asbestos roofs, providing they have not been painted with lead-based paints or coated with bitumen- based material.
Some types of new tiles and freshly applied acrylic paints may affect the colour or taste of rainwater and the first few run-offs may need to be discarded.
As a precaution, chemically treated timbers and lead flashing should not be used in roof catchments. Also, if possible, rainwater should not be collected from parts of roofs incorporating flues from wood burners.
Overflows or discharge pipes from roof mounted appliances such as evaporative air conditioners or hot water systems should not be allowed to discharge onto the roof catchment area or gutters.
First-flush diverters are recommended to prevent the first rains after a dry period from flowing into the tank. This will reduce the amount of dust, bird droppings, leaves and debris that have accumulated on the roof from being washed into the tank. Alternatively the tank inlet could be disconnected so that the first run-off of rain after a dry spell is not collected.
Regular chemical or microbiological testing of domestic rainwater tanks is not necessary and in most cases is not recommended.
Rainwater used for any commercial purpose (such as a food premise) or for community based-supplies (such as hospitals, schools, caravan parks) requires routine testing to ensure that the water is suitable for drinking and is unlikely to cause physical harm through consumption. Regular testing should form part of a documented risk management plan for the water supply.
All microbiological and chemical testing of rainwater must be carried out by an approved provider and compared to the values contained in the current Australian Drinking Water Guidelines. Approved testing providers include:
E. coli should not be detected in a minimum 100 mL sample of drinking water.
The detection of E. coli indicates that maintenance is inadequate and requires investigation. The rainwater tank should be chlorinated prior to further use.
If chlorination is not an immediate option, an alternative source of water should be used for drinking and food preparation or the rainwater should be boiled prior to use.
Roof catchments should be kept clean and clear of leaves and debris and Overhanging branches should be removed. Gutters should be regularly inspected and cleaned if necessary. The use of screens/guards should be considered and all screens should be cleaned regularly.
Water ponding in gutters must be prevented as it can provide breeding sites for mosquitoes and could lead to eggs being washed into tanks. 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 (5 mL) of domestic kerosene. However, kerosene should not be used in AquaplateTM or some plastic tanks. Prevention of mosquito access is the best control option.
Tanks should be examined for accumulation of sludge at least every 2 years. If sludge is covering the bottom of the tank it should be removed by siphon or by completely emptying and rinsing the tank. Professional tank cleaners are available in some areas. Excessive sludge is a sign of inadequate maintenance of the catchment area (roof and gutters).
Regular disinfection should not be necessary. If it is suspected that water in the tank is contaminated, it can be disinfected using 40 mL of liquid sodium hypochlorite (12.5% available chlorine) or 7 grams of granular calcium hypochlorite per 1000 litres of water. Although a chlorine taste and odour may persist for a few days, the water is safe for drinking.
If E. coli is detected in a minimum 100 mL sample of drinking water, the rainwater tank should be chlorinated prior to further use.
Stabilised chlorine should not be used.
The size of tank required to provide the primary or total supply of household water will depend on a number of factors including the amount and pattern of rainfall, roof area and water usage.
To calculate what size tank is suitable for your household refer to the Guidance on use of rainwater tanks.
Before purchasing or installing a rainwater tank check whether there are any local health, building or planning regulations that apply to tanks in your area. In some areas there may be minimum storage and pump requirements for fire fighting.
A mandatory rainwater tank policy exists for new homes and some extensions to existing homes built after July 2006.