Cold water tanks - making water safe to drink

Likely health risks


Pathogens are harmful micro-organisms including viruses, bacteria and parasites which can contaminate drinking water supply.  Generally these come from human and animal faeces and contaminate water from sources such as a leaking septic tank or onsite waste water management system. Poorly maintained onsite waste water management systems can also contaminate other water sources, such as nearby streams or bores. Pathogens from run-off from farming activities can contaminate water in irrigation channels and streams, making it generally unsuitable for drinking if not properly treated. These pathogens are not visible to the naked eye and may be present in water that appears to be clear.

Drinking water that contains pathogens causes gastroenteritis. Children, older people and people with suppressed or weakened immune systems are the most vulnerable to these pathogens. You can reduce the risks by ensuring your drinking water comes from a reliable source and by regularly maintaining your water supply system.


Chemical and heavy metals contaminants can also pose a health risk. These are usually less common than other contaminants such as:

  • Soil from previous industrial, mining or agricultural activities, which may contain contaminants. Dust can be blown on your roof and washed into your rainwater tank, leading to chemical residues and other contaminants that can build up in the water over time.
  • Crop dusting, which can result in agricultural chemicals entering rainwater tanks from roof catchments, irrigation channels, streams and dams.
  • Residues from solid wood fired heaters, which can condense near flues on your roof.
  • Residue from lead-based paints or lead flashing on older roofs and gutters which can wash into your rainwater tank.
  • Run-off from roofs in urban or industrial areas, containing chemical pollutants from the air.

In some parts of Tasmania, groundwater may contain elevated levels of substances such as arsenic and nitrates. Materials used to manufacture tanks (such as lead solders or non-food grade sealants) can also be harmful to your health.

Dealing with dead animal carcasses in water tanks

  • Dead animals in your tank will not necessarily cause illness if you drink the water, but it is best to drain all water from the tank as a precaution.
  • Wash out any sludge from your tank, repair any holes in the roof, and scrub the interior with a household bleach solution.
  • Maintain good ventilation whenever you are cleaning out any tank and always work with an assistant outside the tank.
  • Refill your tank with good quality water and disinfect it with chlorine (as detailed above).
  • If good quality water is in short supply and it’s not feasible to drain and refill the tank, remove as much of the animal carcass as possible and disinfect the water with chlorine (as detailed above).

Insects in water tanks

Mosquitoes often breed in water tanks. Screening inlets and overflow outlets with fine mesh are the best options to prevent mosquitoes from entering your tank.

If mosquitoes are already breeding in your tank, add a small amount of domestic kerosene or liquid paraffin. Use one teaspoon of kerosene in a 1 kilolitre water tank or 3 teaspoons in a 10 kilolitre tank; double these amounts if you are using liquid paraffin.

  • Do not use industrial or commercial kerosene.
  • Do not use kerosene in tanks with a liner or lined with a polymer coating.

If in doubt, check with your tank supplier.

Water tanks after a bushfire

Bushfires generate large amounts of smoke, ash and debris, which can settle on your roof. Generally this doesn’t represent a health risk, although it may affect water colour, taste and odour. If your area has been affected by a bushfire, remove ash and debris from the roof and ensure the first flush of rainwater is not collected in your tank.

New tank - metallic taste

Zinc from a newly galvanised tank might give an unpleasant metallic taste to the water for a while, but is not harmful.

Concrete tanks - pH levels

Water pH tends to rise when stored in new concrete tanks, due to the leaching of lime from the concrete surface. You may need to flush these tanks before their first use.

Making sure your water is safe to drink

To significantly reduce the risk of pathogens, chemicals or heavy metals in your drinking water supply, collect and store your water so that contamination from human, chemical or animal sources is minimised:

  • Ensure surface run-off, irrigation water, leakage from on-site waste water management systems, other drainage systems and/or underground seepage cannot enter your drinking water supply. If possible, store drinking water in an above ground tank rather than an underground tank. Make sure your drinking water plumbing is completely separate from all other plumbing or pipe systems on your property, and all pipe joints are properly made.
  • Do not collect your drinking water from:
    • recently painted roofs (wait until after the first few rainfalls),
    • timber roofs preserved with chemicals,
    • roofs coated with lead-based paints or tar-based coatings, or
    • parts of roofs near flues from solid wood heaters.


  • Regularly clean your roof and gutter -  remove leaves, animal remains, dust and other debris. Install simple screens between your roof and the tank, or use a gutter guard or leaf diverter. The first rainfall after a dry period usually collects most of the contaminants on your roof. Installing a ‘first flush’ or other diversion system will prevent this water from entering your tank. Store this first flush water separately and use it for non-drinking purposes such as garden watering.
  • Over-spray by aerial chemical spraying - divert the collection pipe from your rainwater tank to prevent any chemicals from entering it. Clean the roof or wait until after the next few rainfalls before reconnecting your drinking water tank to your roof.
  • Reduce algae - minimise algae growth by sealing your tank to prevent insects, small animals, birds and sunlight entering.
  • Accumulated sludge - regularly maintain your water tank and clean out accumulated sludge from the base of the tank. You should check your tank for sludge accumulation every two to three years. For advice on de-sludging your tank, read enHealth’s Guidance on use of rainwater tanks available from the Federal Government Department of Health (external link).
  • Bore water - make sure any bore you use as a source of drinking water is properly cased, with an above ground wellhead.
  • Disinfecting - always disinfect your water supply if you suspect it has become contaminated with pathogens.
  • Get advice - consult the installer or manufacturer of your bores, roofing material, tank systems or ancillary equipment for specific advice you may need. Pipes and water tanks should meet the relevant Australian Standards for materials that come into contact with drinking water. You can check this with your plumber, supplier or manufacturer.

Filtering your water

Generally, water that is cloudy or dirty will not be suitable for drinking unless it is properly treated. It is usually more cost-effective to get your water from a good quality source than to treat poor quality water so it is safe to drink.

However, if your drinking water supply does require filtration, make sure the filter complies with the relevant Australian Standards. You can check with your plumber, supplier or manufacturer and follow the maintenance instructions.

Disinfecting your water

In most rural areas of Tasmania, rainwater collected from a clean roof and securely piped into a well-maintained above ground tank shouldn’t need to be disinfected.

Groundwater from cased deep bores also shouldn’t need disinfection.

Groundwater from a shallow bore should be disinfected in case the bore has been contaminated with farm waste or effluent from septic tanks.

If you suspect your water supply has become contaminated with pathogens, you should disinfect it before using it for drinking, preparing food, making ice or personal hygiene.

How to disinfect your water

Inexpensive and effective options include boiling the water that you drink and adding chlorine to the water supply. These are detailed below.

Another option is using ultraviolet light. However, ultraviolet light systems require very clear water to work effectively, and must be carefully designed, maintained and operated.

Boiling water

  • Bring the water to a rolling boil - use an electric kettle with an automatic shut-off
  • Allow the water to cool before storing it in a clean container until use

Adding chlorine to water

  • Follow the manufacturer's measurements - Do not adjust the chlorine to water dosage.
  • Follow the safety and handling instructions on chlorine containers.
  • Wear proper hand and eye protection when handling or preparing chlorine solutions.
  • After chlorinating, you should ideally wait at least 24 hours before using the water to allow the pathogens to be destroyed. The chlorine may leave the water with a harmless taste and odour, but this should disappear in around 10 to 14 days. Boiling the water will also remove most of this taste and odour.

Water testing

Generally, your drinking water supply shouldn’t need to be tested if it is well managed and maintained. However, if you do need your water tested, most analytical laboratories can provide this service. You can find a list of water testing laboratories on the Department of Natural Resources and Environment Tasmania website.

Fluoride in private drinking water supply

Fluoride is added to many town water supplies to help protect teeth against decay. Rainwater will not contain fluoride; some groundwater supplies may.

If your drinking water supply doesn’t contain fluoride, it is especially important to look after your teeth through healthy eating, regular brushing with fluoridated toothpaste (although children under the age of two should not use fluoridated toothpaste without dental advice), and regular dental check-ups.

For more information on fluoride, call the Department of Health and Human Services on 1300  135 513.

Related information

Updated: 16 Sep 2022

This page has been produced and published by the Consumer Building and Occupational Services Division of the Department of Justice. Although every care has been taken in production, no responsibility is accepted for the accuracy, completeness, or relevance to the user's purpose of the information. Those using it for whatever purpose are advised to verify it with the relevant government department, local government body or other source and to obtain any appropriate professional advice. The Crown, its officers, employees and agents do not accept liability however arising, including liability for negligence, for any loss resulting from the use of or reliance upon the information and/or reliance on its availability at any time.