Public Health after a Cyclone or Large Rain Event


If in doubt about the safety of drinking water, boil water before consumption.

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 purposes. 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 four 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.

Swimming Waters

After a flood or large rain event, swimming waters – including beaches, estuaries and rivers – are likely to be contaminated with pollutants from streets, sewage and chemicals that are washed into waters via stormwater systems. There is an increased level of harmful bacteria, unpredictable currents, fast flowing water and submerged hazards that are very dangerous. Swimming should be avoided for at least 1-2 days after heavy rains.

Never swim in or attempt to drive through floodwaters.


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

After a flood or heavy rain, 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. Fish 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 with levels of between 2-5ppm 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.

Septic Tanks 

Flood waters or heavy rains may affect your septic tank system, which is also known as an onsite wastewater system. Failed systems are not easy to identify. However, some simple indicators may include:

  • a pungent odour around the tank and land application area.
  • blocked fixtures, with wastewater overflowing from the relief point.
  • high sludge levels within the primary tank.
  • sewage flowing up through the toilet and sinks.

Some onsite wastewater treatment systems may rely on mechanical and electrical equipment, such as pumps, aerators and filters. This equipment may be damaged by flood or loss of power.

To prevent injury or further damage to your system contact your service agent.

If your system is not operating properly or you are unsure do not use any toilets, laundry, kitchen, bathroom or clean-up equipment connected to the onsite wastewater disposal system until all parts of the wastewater treatment and disposal system have been professionally inspected and repaired.

How can my septic tank be repaired?

Only trained specialists are suitably equipped to clean or repair onsite waste disposal systems. This is because tanks may contain dangerous gases and other harmful materials.

Aerated wastewater treatment system

Aerated wastewater treatment systems (AWTS) should not be used if it has been inundated with floodwater. Isolate the electrical connection and call the service technician immediately.

Sewage overflows

In all situations where a sewage overflow (also referred to as wastewater overflow) clean up procedure is needed for your property, persons involved in the clean-up procedure should wear personal protective clothing such as rubber boots, rubber gloves and washable or disposable coveralls. Unprotected persons should be evacuated from the affected area until the area has been thoroughly cleaned and disinfected. Other safety precautions to be followed include:

  • Assume anything touched by wastewater is contaminated.
  • Immediately wash and disinfect any wounds that come into contact with wastewater.
  • Change out of dirty clothes and wash clothes separately.
  • Clean and dry dirty footwear.
  • Contact your doctor immediately if you experience any illness.
  • Wash your hands and affected areas of the body thoroughly with clean warm water and soap, especially before eating or smoking.

Mosquito Control

Stagnant water left behind by floods and rain provides an excellent breeding ground for mosquitoes.

This increases the risk of mosquito-borne diseases such as Ross River virus (RRV) and Barmah Forest virus (BFV). In the north of Western Australia there is also the potential for the rare, but potentially fatal, Murray Valley encephalitis (MVE).

Mosquitoes can breed around your home, they will lay their eggs in fresh or salty water, and often in containers that hold water. Common breeding sites include pot plant drip trays, gutters, ponds, pet water bowls, old tyres, rubbish, containers and pools that are not well maintained.

Stop mosquitoes breeding around your home by following these simple steps:

  • empty out or discard containers and rubbish that may hold water.
  • clean out roof gutters to prevent water from pooling.
  • empty, clean and refill bird baths, stock troughs and pet water bowls at least once a week.
  • keep swimming pools properly maintained and free of debris.
  • empty wading pools at the end of each day.
  • stock backyard ponds with fish to eat mosquito larvae.
  • cover rainwater and septic tank openings, wells or other large water containers with mosquito-proof mesh.
  • keep edges of ponds clear of vegetation.

You can make a difference by preventing mosquitoes breeding around your home.

Food safety after cyclones, floods and other disasters

When disasters cause the power to go out, it generally means the food in your fridge will start to go off.

Unless food can be stored below 4 °C within 2 hours of a power cut, all potentially hazardous foods like meat and dairy  that are typically stored in the fridge need to be placed in alternative cold storage, eaten immediately or disposed of appropriately. If in doubt, throw it out !!!!!!

Floodwater may have contaminated your vegetable or herb garden with bacteria, chemicals or other dangerous substances. Some vegetables may still be all right to eat. The Department of Health recommends disinfecting in hot water, peeling and cooking the produce to prevent food borne illness. 


Drying out the house after floods or Heavy Rain damage

  • Open doors and windows to let the house air out for as long as possible.
  • Once power is restored use fans and dehumidifiers to dry out the house.
  • Air conditioning or central heating should not be used unless they are undamaged and uncontaminated by the floodwaters. If you suspect contamination with mould or floodwaters, do not use these systems until they have been cleaned and checked by a qualified person.

Mould removal efforts should focus on:

  • removing all sources of pooled water or excessive moisture from the home.
  • removing all wet or flood damaged materials or items that cannot be adequately dried or cleaned, including: wallpaper, plasterboard, carpet rugs, bedding, mattresses, furniture, stuffed toys, clothing, wet or damaged materials.
  • removing all porous (soft or absorbent) materials with mould growth.
  • temporarily storing damaged or discarded items outside the home (in a safe, clean, dry place such as a shed or garage) until your insurance claim is processed.
  • cleaning and disinfecting all affected surfaces inside the house, including: floors, walls, kitchen, bathroom, laundry.
  • allowing the house to dry throughout by airing or active drying (for example fans or dehumidifiers).

Cleaning up mould

  • If you intend to clean up mouldy areas it is recommended that you wear a shower cap,  goggles and P1 or P2 particulate face respirator, to prevent breathing in mould spores.

Injury prevention and bacterial infections

Water, mud and silt can contain a range of bacteria and viruses that can make you or your family sick. Illnesses may include:

  • diarrhoea.
  • gastroenteritis.
  • skin infections.
  • soft tissue infections.

Heavy rains can make surfaces such footpaths, roads and floors very slippery. Fall injuries are not unusual during clean-ups. Hazards also can occur when cyclonic winds lift a range of materials and debris such as:

  • fences.
  • roofs.
  • electricity wires.
  • cars.

It is important that you take proper precautions to prevent illness and injury:

  • Always wear protective clothing, such as boots, gloves and a face mask when cleaning.
  • Do not expose broken skin or cuts to dirty water, mud or silt.
  • Do not use petrol or diesel-powered equipment, such as generators or pumps, in enclosed spaces.
  • Be alert to snakes, spiders and rats that may have taken refuge in your home.
  • Make sure your immunisations, especially tetanus, are up-to-date.
  • Always wash your hands and any part of your body that has been exposed to dirty water, mud or silt, especially before eating or preparing food.
  • Wear a mask when working with heavy mould.
  • Never touch electric wires, even if you think they are not live.

You need to seek medical attention if you do become ill or injure yourself, particularly if any cut becomes painful and red and if you develop a fever.