Water safety after cyclones, floods and other disasters

Drinking water

Sometimes following a disaster, a boil water alert is issued for areas connected to mains scheme water because the mains water may be unsafe to drink or cook with.

If a boil water alert has been issued, it is essential you follow this warning to prevent illness.

To prepare water for drinking and food preparation, you should heat the water to a rolling boil for at least 1 minute using a stove or kettle and then allow it to cool. This will help to kill any bacteria.

Be sure to keep children clear from any boiling water until the water has cooled down to room temperature.

Once it has cooled it should be placed in the fridge in a clean container with a lid.

Under no circumstances should you drink or cook with water that has not been boiled until the alert is lifted.

Alternatively you can use bottled water.

Cooled boiled or bottled water should be used for:

  • drinking
  • cooking
  • washing raw foods (such as seafood or salads)
  • making ice
  • cleaning teeth
  • your pet’s drinking water.

If a boil water alert has been issued:

  • dishes should be washed in hot soapy water or in a dishwasher
  • children should take bottled or cooled boiled water to school.

Your local radio station or local government authority (external site) will provide updates. Check their websites for information.

When the boil water alert is lifted, you will need to follow the water supplier’s instructions for flushing the household water pipes.

Find out more about emergency treatment of water supplies.


Flooded or damaged rainwater tanks may be contaminated.

Tanks may also become breeding areas for mosquitoes.

Action should be taken, as soon as is safe to do so, to ensure mosquitoes are prevented from breeding in these tanks.

In instances where the water is too dirty and cannot be saved, the tank should be drained.

Where the water in the tank can be saved, it needs be properly disinfected.

After a bushfire

Learn more about using rainwater tanks after a bushfire and what you need to do if your tank has been contaminated by:

  • ash
  • smoke
  • debris
  • fire
  • fire fighting activities.
Bore water

Following flooding, the condition of a garden bore system or water storage tank may be compromised by floodwater entering the system.

Bore water should not be used for drinking or food preparation following flooding. However, some people use bore water for irrigation or laundry purpose.

If this is the case, you will need to disinfect the water from the bore pump to the storage tank. The following disinfection procedure is recommended.

If the tank is clean

If the storage tank is clean, add 1.5 grams of dry pool chlorine per 1000 litres of water to ensure it is safe to use.

If the tank has been contaminated

If the tank has been contaminated you should add 150 grams per 1000 litres for turbid (cloudy) water or 75 grams per 1000 litres for clear water.

The mixture should be left to stand in the tanks for 4 hours.

The tank should then be drained. Do not drink this water.

You can now refill the tank adding 1.5 grams of dry pool chlorine per 1000 litres.

Recreational waters, eating shellfish and fishing

Recreational waters

After a flood, recreational waters – including lakes, rivers, estuaries and beaches – are likely to be contaminated with sewage and chemicals.

There may also be unpredictable currents, fast flowing water and submerged hazards that are very dangerous.

Never swim in or attempt to drive through floodwaters.

Read more on tips for healthy swimming.


Shellfish includes oysters, mussels, clams, pipis, scallops, cockles, and razorclams.

After a flood, it is almost certain that harmful microorganisms and toxins will be present in waterways (including rivers, lakes, estuaries and the ocean) due to run-off from the land. Do not eat shellfish from flood affected waters as they can make you sick.


Fish caught during flood periods should be rinsed prior to scaling and filleting.

Brown water in swimming poolFish should be cooked thoroughly. You should avoid cross contamination between raw and cooked fish.

Swimming pools

Following a disaster, swimming pools should either be emptied or kept chlorinated to prevent the water quality from deteriorating.

Contaminated swimming pools can be:

  • a source of odours and bacteria
  • a breeding place for mosquitoes
  • a risk to people who use them.

More information

Public Health

This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.

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