Floods are the most frequent natural hazard in Canada and most floods are due to heavy or prolonged rainfall or snowmelt.

After a flood, it is important to restore your home as soon as possible to protect your health and prevent further damage to your house and its contents.

Flooding may cause damage to the structure of the house and can also contain sewage (particularly in rural areas), that may pose a serious health hazard. Dug or drilled wells may also be contaminated by flood water. Another concern from flooding is the possible growth of mould or bacteria in the flood-damaged areas of your home that could contribute to adverse health effects.

What are the public health dangers related to flooding?

Food contamination

See food safety

  • Food temperatures may not have been maintained (due to a power outage, for example)
  • Food may come into contact with flood water

Water contamination 

See drinking water

  • Overwhelmed drainage, water treatment and sewage systems 
  • Flood waters can contaminate dug or drilled wells 
  • Pollutants such as agricultural waste, chemicals, raw sewage or metal can contaminate local water sources
  • Sewer systems can back up into household plumbing systems
  • Flood contaminated water can carry organisms that can cause disease (e.g. bacteria, viruses)

After a flood, your well/cistern water may be contaminated with bacteria and chemicals that can make you sick.

First steps

  • Stop using your well water for drinking, cooking, and washing yourself.
  • Use bottled water. Boiling water for at least one minute is only safe if the well/cistern is not contaminated with chemicals or heavily polluted with sewage.

Remember, drinking water includes water used for drinking, making artificial milk (formula) for babies, juice, and ice cubes; washing fruit and vegetables; and brushing your teeth.

  • Stay away from your well pump when it is flooded--you could get an electric shock.
  • Do not rely on the well water treatment equipment or devices after a flood. Hire a certified well contractor to check your well and its wiring and to restart the well pump, if needed.
  • Do not drink the water or use it for food preparation until laboratory testing shows that it is safe for drinking.
  • Bacterial testing is free through Region of Waterloo Public Health. Visit our Private Well Water web page for more information; or speak to a Public Health Inspector at 519-575-4400


See indoor air quality

  • Flooded buildings become damp and create a perfect environment for bacteria and mould growth

What can you do?

Avoid illnesses from food contamination

See power outages

  • Throw away perishable foods (including meat, poultry, fish, eggs and leftovers) in your refrigerator when there is a power outage longer than four hours (see When to Save and When to Throw Out chart)
  • Throw away food that may have come in contact with flood or storm water or if the food has an unusual odour, colour or texture (Remember: food contaminated with bacteria does not always smell or look bad)
  • Be prepared by having a cooler and ice ready to keep refrigerated food cold during a power outage
  • Have canned goods available - canned goods will keep for long periods of time, for as long as two years (milk, meat, vegetables, and fruits can be purchased in cans and do not require cooking) 

Avoid diseases spread through water contamination and sewage backup

  • Boil your water for one minute before drinking it if there is a boil water advisory in effect 
  • Add eight drops of household bleach to one litre of drinking water, stir and let stand for 30 minutes prior to consuming 
  • Avoid drinking dirty or bad smelling water (even if there is no boil water advisory) 
  • Store bottled water at home for emergencies

Reduce mould in your home

  • Seek professional help to clean and remove large areas of mould 
  • Remove damp items 
  • Use dehumidifiers to dry damp areas (if the dampness is not severe)
  • Wear protective masks while cleaning areas with mould

Links and resources

Public Health Agency of Canada - Climate Change, Floods, and Your Health

Ministry of Health and Long-Term Care - Flooding and Your Health

Government of Canada - Get Prepared: Flood Information

Grand River Conservation Authority - Flood Warning System

Click here for information about how to subscribe to receive flood advisories and warning messages from the Grand River Conservation Authority

You can also receive notices of Grand River Conservation Authority flood advisories and warning messages through their Twitter feed at grca_flood_msg

For more information, please call 519-575-4400, ext. 5147.