Guidance for Well Owners During and After a Flood

During a flood, flood water may enter private wells. When this happens, the water within the well can become contaminated. The contamination may be from waterborne pathogens (germs) that can cause serious illness to humans or pets, or from chemical products released during the flood such as debris, fuel or oil.

During the flood

Do not drink or use well water during the flood. You must use an alternate source of safe drinking water (such as bottled water) for all your needs.

You CANNOT use the water for:

  • drinking
  • making ice cubes, juices or other mixes
  • preparing baby food or infant formula
  • food preparation, including washing fruits and vegetables
  • gargling or brushing teeth or dentures
  • washing your hands (You may use alcohol-based hand disinfectants containing more than 70 % alcohol in situations where an alternate source of safe water is not available.)
  • washing dishes, cutting boards and countertops
  • household cleaning
  • doing the laundry
  • taking a shower or a bath
  • swimming
  • any other use

Boiling the water will NOT make it safe to drink as boiling does not remove chemicals that could potentially be present in the water.

After the flood

As the well owner, you want to ensure the safety of your well. If a laboratory analysis of water samples from the well shows that it is producing water that is not potable (not safe to drink), then you must follow the advice to bring the well back into service safely, or take appropriate action.

Inspecting Your Well

EXERCISE EXTREME CAUTION when approaching and inspecting your well after a flood, especially if your well is older or a large diameter dug well. The ground around the well may have eroded during the flood, possibly creating unsafe conditions. In some cases, the electrical wires attached to the pump in a well may have become damaged, risking electrocution. Check the well to identify any potential hazardous conditions or pathways for surface water and contaminants to enter the well.

Flushing Your Well

Remove any debris from the well. Once you are sure that your well pump and its electrical components are in operating order, pump the well to reduce any flood water that may have gotten into your well. The length of time you need to flush your well depends on the depth of your well and the amount of water you are able to flush at one time.

Disinfecting Your Well

After flushing your well, it should be disinfected by treating the well with properly prepared chlorine solution, and discharging the heavily chlorinated water from the well and the plumbing.

There are some safety considerations when working on a well and many technical steps to properly clean and disinfect a well. Therefore, to bring your well back into service safely, you should consider retaining the services of a qualified professional to evaluate and service the well and the well pump:

  • For a drilled well: qualified registered professional or a licensed well driller
  • For a dug well: qualified registered professional or a licensed well digger
  • For a well pump: a licensed pump installer and, if necessary, a certified electrician

Testing Your Well Water for Contamination

Have your well water tested for pathogen contamination as soon as possible. The EOHU offers free bacterial well water testing for residential systems. If a septic system is located nearby, you should also ensure that the septic system is in good working order and not damaged due to flooding which could potentially contaminate your water source. Further biological testing may be recommended.

If bacterial contamination problems are identified, the EOHU will advise of the treatment process that must be initiated to achieve potable water on an individual basis. The EOHU may recommend that you hire a qualified registered professional, such as a licensed well driller, to evaluate and service the well. For instructions on how to ensure that your water is safe to drink in the meantime, see the information below.

If test results show that there are no bacterial issues with your well water sample, you can begin using your well. However, if you suspect that there are signs of other possible contaminants after flushing/pumping, such as residual visible debris, changes in colour or clarity, petroleum or diesel odour, you should not use the well water, and should contact the EOHU or the Wells Help Desk of the Ontario Ministry of Environment and Climate Change (MOECC) at 1 888 396-9355 for further instructions.

Drinking Water Safety –- Possible Bacterial Contamination

If you do not suspect chemical contamination, and are only concerned with bacterial contamination, follow these instructions until water tests show that your well water is safe for consumption.

Use boiled water or an alternate source of safe drinking water (such as bottled water) for:

  • drinking
  • making ice cubes, juices or other mixes
  • preparing baby food or infant formula
  • food preparation, including washing fruits and vegetables
  • gargling or brushing teeth or dentures

Bring water to a rolling boil for at least one minute. Let water cool before using or drinking.


  • Wash hands with bottled water, or boiled then cooled water.
  • If using non-boiled tap water, wash hands with liquid soap and dry thoroughly. Then rinse/sanitize using one of two solutions:


  • Toddlers and young children should not take baths or showers as they are likely to swallow water. Give sponge baths instead.
  • Adults, teens and older children can safely take showers.

Washing and Cleaning

  • Dishes, cutting boards and countertops can be washed with soap and water and then disinfected with a strong bleach solution
  • Laundry can be done as usual.

You can resume drinking your well water once tests have shown that the water is safe for consumption.

Useful links:

For more information:

Wells Help Desk
Ministry of the Environment and Climate Change
1-888-396-WELL (9355)

Eastern Ontario Health Unit