Flooding can happen without warning and when we least expect it. There are potential health risks associated with contaminated flood water such as the spread of gastroenteritis (diarrhoea and vomiting). The information below should be useful to help protect the health of you and your family and whānau during and after a flood event.

Personal Safety and Hygiene

Always assume that all flood water is potentially contaminated with farm run-off, faecal matter from animals, and sewage. Children in particular must keep away from flood waters.

The best advice is to keep away from flood waters, use only a clean water supply for drinking, cooking, and washing. Hand washing is always vitally important to help prevent the spread of disease.

Hands must be washed with soap and water and dried properly after any contact with flood water, flooded property, after going to the toilet, and before preparing or eating any food. 

See this information sheet for information on how you can Keep the Bugs at Bay after a flood.

Food Safety

  • Always wash hands with clean water and soap before and after preparing food.
  • Do not eat foods that may have gone off.
  • Use clean water to wash vegetables and fruit.  If you are unsure if the water is clean, boil water for at least 1 minute, then cool.
  • Do not eat garden produce if the soil has been flooded as the food may be contaminated.
  • If the power is cut off, use the food in the refrigerator first, then food in the fridge-freezer, then food in the chest freezer.  Get rid of all foods needing refrigeration when they have been unrefrigerated for more than two hours.

For further information on how to help protect you and your family from getting sick from food following a flood check out, Food safety in natural disasters and emergencies from the Ministry for Primary Industries.

Drinking Water

If a 'boil water' notice is issued by your water supplier, then water needs to boiled before drinking and brushing teeth. This means that the water needs to be brought to a rolling boil for at least 1 minute before it becomes safe to drink. 

The quality of water supplied may be compromised during a flood. 

If you have concerns about the safety of your water supply, please visit the following web pages:

People who supply their own water should contact a local environmental health officer at their local council for advice if they are concerned about the quality of their water. They can also follow the advice on the web pages above.  



In some emergency situations the water supply may be cut off, or water and sewage lines may be damaged, and you may need to use improvised emergency toilets.

How to make an emergency toilet with a container:

  • Use a watertight container such as a rubbish bin or bucket, with a snug-fitting cover.
  • Pour or sprinkle a small amount (such as a teaspoon full) of regular household disinfectant or bleach into the container after each use to reduce odour and germs. Keep the container covered.
  • If you need to store the waste before it can be disposed of, place it in a larger container with a snug-fitting cover until services are restored and it can be disposed of in the usual way. 


Flood-Damaged Houses and Buildings

There are potential health risks associated with contaminated flood water. It can be assumed that all flood water is potentially contaminated with farm run-off, faecal matter from animals, and, in some cases, sewage. Where a home, office, or retail premises has been affected by flood water above floor level, all soft furnishings will need to be effectively decontaminated or disposed of. This includes carpets, curtains, soft furniture, and any other fittings. In some cases thorough cleaning (i.e boiled or washed and treated with a disinfectant) followed by exposure to sunlight will be sufficient, but some furnishings and fittings will have to be thrown out. Each situation needs to be assessed individually.  Anything that is discarded should be disposed of appropriately rather than leaving it lying around for weeks. A general rule is if you can’t put a soft furnishing in a washing machine it must be thrown out. If any food is affected by flood water, or fridges or freezers were left without power such that food has not been chilled for more than two hours, this food will need to be thrown out. Any food premises will have to take extra care to ensure everything is decontaminated.

  • Cleaning and disinfecting hard surfaces
    Hard surfaces (e.g. hard floors, tables and benches) that have been covered with flood waters must be cleaned before being used again.  Start by scrubbing all hard surfaces with soap, such as dishwashing liquid, and water until all visible dirt is removed. Once surfaces appear clean wipe all surfaces again with a disinfectant. Always follow the directions on the bottle, wear gloves and ventilate the room by opening windows. 
  • Dust nuisance
    Dust from dried out flood water can be irritating and cause nuisance for those cleaning up. Practical measures can be taken to keep dust to a minimum.  Keep any area being swept moist and where possible work upwind.

    Mask-wearing is recommend if you have respiratory issues but is otherwise optional when cleaning up after a flood event (see below for mask recommendations when cleaning mould). However, masks can be useful in filtering out dust which may make working more comfortable.

    Anyone experiencing significant symptoms from exposure to dust should contact their usual family doctor or call Healthline on 0800 611 116.
  • Mould
    If mould has developed on surfaces, take extra care when cleaning to reduce the risk of infection. Wear protective clothing, including an N-95/P2 mask and rubber gloves. Masks are available from hardware shops and chemists. Clean the mould off as soon as possible. Use soap and water to clean the surface then apply a commercial mould product or household bleach solution. For large areas you may need to call in a mould removal specialist.

   Redecorating should be delayed for at least three months after any repairs to prevent the risk of mould being covered.

   See this information sheet regarding What to consider when returning to your home after a flood.

Sewage Contamination Concerns

The sewage system is often affected in a flood. Most small rural communities rely on septic tank systems for collecting, treating, and disposing of sewage. The tank itself can be affected by flood waters, and its contents can find their way to the surface and mix in with the flood waters. In larger towns and cities there is a network of sewer pipes connecting each building to a single sewage treatment plant. Occasionally the network of pipes can be broken by flooding, or one or more of the pumps that are used to pump sewage through the pipes may fail. When things go wrong with a sewage system this usually results in flood waters being contaminated. Avoid contact with flood waters. Children in particular must keep away from flood waters. 

Flooded Sports Fields, Parks and Gardens

Any sports fields, parks, or gardens which have been flooded should not be used until 48 hours after all surface water has disappeared.  This time allows for the action of the fresh air, the wind, and sunlight to decontaminate most of the bugs that would have been left behind by the flooding.  Of course our environment is not sterile.  There are always bacteria, viruses, and other microbes all around us.  This is why we must always wash our hands after playing or working outside, and before cooking or eating.

Recreational Water

As a public health precaution, it is routinely recommended that people avoid swimming in rivers, streams and harbour areas for at least 48 hours after a heavy rainfall. For flood events, this should be at least 72 hours after rivers have returned to normal flow and colour. 



Shellfish beds are likely to be affected by contaminated flood water.  Because of the way most shellfish filter their food from the water in which they live they are likely to all carry higher than acceptable levels of microbes, including bacteria and viruses, for some time. Read more about shellfish.


Flooding may lead to a temporary increase in the number of mosquitoes and flies. Residents are advised to use insect repellent to help avoid being bitten and to tip water from containers around their properties.

Self Care and Wellness

It’s normal to feel upset after extreme weather events. If you need support or advice, or have feelings of anxiety, stress, prolonged fear, hopelessness or anger and need to talk with someone, you can phone Healthline on 0800 611 116.

The below resources may also be helpful:

Other Health Concerns

Anyone experiencing any illness should consult their family doctor as usual or Healthline on 0800 611 116.    


Further information