Public health authorities issued rainwater tank advice to residents returning to their homes in bushfire areas in Tasmania, particularly around Molesworth, on 13 February 2013.
State Manager of Environmental Health Stuart Heggie said the risk to human health is low from contaminated rainwater tanks in bushfire-affected areas, but returning residents should still take precautions.
"While the risk to human health is low from contaminated water, it is important residents take some simple precautions," Mr Heggie said.
"If the water from your rainwater tank looks, smells, and tastes okay, it should be fine to use.
"But if the rainwater looks, smells or tastes unusual, assume it is contaminated and don't drink it or use it for cooking or preparing food.
"The water can be used for other purposes including flushing toilets, dampening dust and ash and watering, though not for watering fruit and vegetables."
Mr Heggie said bushfires generated large amounts of ash and debris that could contaminate rainwater supplies.
"Although the presence of ash and debris from burnt forests in rainwater does not represent a health risk, it can affect the colour, clarity and taste of rainwater," Mr Heggie said.
"And there may be other debris on your roof or washed into your tank which may be harmful, including animal carcasses and trace chemical residues from burnt treated timber."
Mr Heggie said the following simple steps could be taken to ensure rainwater supplies are suitable for drinking after a bushfire.
Reducing the risk of further contamination
• Check your roof and guttering for animal carcasses and pieces of timber. Remove them as soon as possible - safely - to avoid contaminants getting flushed into your tank.
• Remove ash and debris from the roof and gutters safely.
• Hose off the roof catchment area if water supplies are available. Use a first flush device or diverter (recommended as a routine installation) between the roof and the tank to prevent ash and other debris from entering the tank and contaminating the water.
• Do not collect this flush water or the first flush of rainwater after the bushfire. You may need to manually divert quite a lot of wash-down water if hosing off the roof, by fully opening the end of the device or propping the diverter to one side.
• If you do not have a first flush diverter, disconnect the inlet from the roof to the tank so the wash-down water runs to waste until the ash and debris has been removed.
• If your rainwater has been contaminated, drain, clean and disinfect the tank and allow it to refill with clean rainwater or fill with water provided by a registered water carter (look under 'Water Cartage' in the Yellow Pages). All commercial water carters must be registered with their local Council.
• If an animal carcass is found inside the tank, safely remove it as soon as possible. Drain, clean, refill and disinfect the tank. It is important to:
o Add the correct amount of chlorine to your tank, preferably when it is filling. It is important that the chlorine is distributed right through the tank for it to be fully effective.
o Wait at least one hour.
o The water should then be safe to drink.
o You might taste or smell chlorine, but it will quickly disappear.
• If draining the tank has to be delayed, remove the remains and disinfect with chlorine in the interim.
Fire retardants and foams
• Fire retardants and foams may be present on your roof if they were used to fight the fire at your house. The recommended concentrations of the commonly used retardants and foams should not present a risk to health, but may affect the taste of the water. Fire retardants also contain detergents that may cause the water in the tank to froth.
To calculate chlorine disinfection rates and tank size: http://www.health.gov.au/internet/publications/publishing.nsf/Content/ohp-enhealth-raintank-cnt-l~ohp-enhealth-raintank-cnt-l-4~ohp-enhealth-raintank-cnt-l-4.2
For more information on the fire situation and support services, contact 1800 567 567.
Up-to-date information on the fires can also be found at the Tasmania Fire Service website www.fire.tas.gov.au
Information on grants and other support available to those affected by fires can be found at www.dpac.tas.gov.au/bushfires
13 February 2013