Well Water After a Flood

If you use well water and you have flooding in your area, your drinking water may be contaminated. Bring drinking water to a rolling boil for at least one minute before use or use another safe water source until you know your water is safe.  Boil water or use another safe water source for:

  • drinking
  • cooking or preparing food
  • making baby food or formula
  • washing dishes
  • brushing your teeth
  • washing your hands
  • bathing or showering
  • making ice, juice, coffee, tea, pudding or other mixes
  • washing fruits and vegetables

You need to inspect your well carefully to assess the impact of the flooding. You may need to repair and/or disinfect your well before using it.

Drinking water wells can also be contaminated by fuel, oil or other chemical products released during the flood (such as from home oil tanks and agricultural tanks). If you think your well may be contaminated by petroleum or other chemicals call Public Health Services at 905-546-2189 or the Ministry of Environment Spill Action Centre at 1-800-268-6060 immediately.

How to get a flooded well back into service

There are four steps to get a flooded well back into service safely: 

A flood leaves warning signs that a well may be unsafe. Check if:

  • the well is located in or near the area that was flooded. Left over debris and mud from the flood and water or mud stains on the well casing can indicate that the well was flooded.
  • the ground surface around the well is intact and stable. During flooding the ground around the well may erode, creating unsafe conditions or a pathway for surface water and contaminants to enter the well.
  • there are any electrical components or wires visible. Visible electrical wires are dangerous and you should avoid them due to electrical shock. If electrical connections or controls located outside the well casing are under water, turning on the pump may cause electrical shock or damage to the system. Contact a qualified electrician for help.
  • there is any visible damage to the well casing.  A bent or cracked well casing may allow surface water, sediment and debris to enter the well and will increase the risk of contamination.
  • the well cap and seal are securely fastened to the well casing.  A loose well cap can allow sediment and debris to enter the well and contaminate it.

Most private wells have the pump located inside the well casing and submerged, so you will probably not be able to inspect the pump. You should contact a qualified professional, registered well driller or pump contractor to evaluate and service your well pump. 

Do not turn on your well pump until the well is assessed and repaired. Do not drink, cook, bathe or shower with well water until the well is disinfected and flushed.

General cleaning

To avoid damage to the well, remove mud, silt and other debris from the well casing, cap and other accessible components. Be sure electricity is off before you clean any electrical components. If excessive mud, silt or sediment has entered the well, you may need to remove the pump before cleaning the well.

Well drainage

Re-grade the ground around the well to direct all surface water away from the well casing. Surface water contains contaminants that can easily get into the well if surface water is allowed to flow down along the well casing.

Well and pump inspection

Floodwater carries large debris that can dislodge parts of the well and distort or crack the well casing. Floodwater may also deposit a large amount of sediment in the well. If you observe any of these conditions you should have a qualified professional repair your system.

Electrical system

If the pump's control box was submerged during the flood, clean and dry its electrical components before electrical service is restored. Make sure electricity is shut off before cleaning electrical components. Consider hiring an electrician to clean and inspect.

Pump operation

If your well pump will not start or pump water after cleaning and general repair, turn off the electricity and get assistance from a registered well technician or pump contractor.

Pumping the well

Pump the well until the water runs clear to rid the well of floodwater, after the well is inspected and cleaned. Use an outside spigot and a hose to direct the water to a nearby drainage way rather than into your septic system or public sewer. Depending on the size and depth of the well and extent of contamination, pumping times will vary. It could take thirty minutes, or it could be several hours or days.

You should disinfect your water well that has been flooded before using it for drinking, cooking, bathing or showering. Even if your well is operational, you should disinfect your water until it is tested and found safe for drinking. Changes in the water's appearance, taste or odour may indicate possible contamination.

Disinfecting water for home use

If your well was flooded, you can disinfect the water to make it safe for drinking and using in food. Here are three different ways to do this:

  • Disinfection by boiling - bring water to a rolling boil for at least one minute; let the water cool before drinking.  Boiled water tastes better if you put oxygen back into it by pouring it back and forth between two containers.  This is the safest method of disinfection.
  • Using liquid chlorine bleach - add eight drops of unscented liquid chlorine bleach (4-6% available chlorine) per gallon of water.  You can add up to sixteen drops if the water is cloudy.  Stir and let stand for 30 minutes. If the water does not taste and smell of chlorine, add another eight drops of bleach and let stand for another 15 minutes.
  • Using iodine or chlorine tablets - check the expiry date on the tablets before you use them.  Follow the directions on the package.
    Usually one tablet is enough for one quart of water but use two tablets if the water is cloudy.

Disinfecting a well

If your well requires disinfection after a flood, pick up Water Wells - Best Practices Management and Keeping Your Well Water Safe to Drink at Hamilton Municipal Service Centres:

If you are unfamiliar with how to disinfect your well, consult with a licensed plumber or well technician.

After you disinfect and flush the chlorine out of the water system, you should test the water to confirm that contamination has been removed. If chlorine odours persist, you may have to do additional flushing or wait several days before testing to be sure that all the chlorine was flushed from the water system.

Until testing shows that the water is not contaminated, you should continue using bottled water or disinfecting water for drinking and food preparation. You may wish to consider re-testing the well water again after several weeks.

If flooding and groundwater contamination is extensive, your well may be susceptible to recontamination for some time.

Protect your well from future damage

There are some improvements you can make to protect your well from future damage:

  1. Get a new well - if frequent flooding occurs, consider drilling a new well where it is not subject to seasonal flooding.
  2. Grading the ground surface immediately surrounding a well casing and, if possible, the property in general, should be graded to divert surface water away from the well. If erosion around the well has been a problem, consider using vegetation or other erosion control measures.
  3. Extend casing to a height above the expected or experienced level of the floodwater to protect against wellhead submersion.
  4. Well cap - install a watertight and vermin-proof well cap.