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Of all natural hazards in Canada, floods are the most frequent and most costly.  They can develop slowly or quickly, in both urban or rural settings.  Besides the obvious risk of drowning, injury and hypothermia posed by floodwater, secondary health threats such as mold, electrocution hazards, as well as drinking water and food contamination can be a result of flooding.

Click on the headings below to learn more about floods as well as what you can do to protect yourself and your loved ones.

Definitions, Types and Causes of Floods

Floods are defined as an overflow or inundation of water from a river or other body of water, or over land, which causes or threatens damage.

There are distinct types of flooding:

  • Flash Flooding: Rapid on-set flooding, where water rises quickly in a short amount of time, with little or no advanced warning. Such flooding can be fluvial or pluvial (defined below) and often features fast-moving waters that can carry large amounts of debris.
    • Riverine (Fluvial): A flood due to higher water levels beyond the channel capacity of a natural or somewhat natural watercourse.
    • Urban (Pluvial): Occurs when rainfall or snowmelt overwhelms the capacity of the urban drainage system or when there isn’t a sufficient overland flow route to move the water away.
  • Storm Surge: Storm surge is defined as an abnormal, sudden rise of sea or lake level due to a storm event.
  • Seiche: A period of oscillation of an enclosed body of water that may result in large waves.  This oscillation is commonly referred to as ‘the bathtub effect.’
  • Coastal Flooding (from Lake Erie): Although rare, has historically caused less severe instances of flooding in Ontario.



Flooding can be caused by:

  • Extreme rain
  • Snow melt
  • Ice break-up
  • Soil moisture conditions
  • Ice jams
  • Frazil ice
  • Natural dams
  • Structural failure of dams


Floods can develop slowly or quickly.  Flash floods can come with little or no warning.


Common Local Causes

Flooding caused by extreme rain is more common in southern Ontario due to this region experiencing a higher number of heavy rainfall events.

Sieche events have occurred during storm surges or periods of high winds when Lake Erie water levels are elevated.  In these instances, flooding starts in low-lying areas on the northern shoreline (e.g. Port Dover, Turkey Point) and, when the wind dies down or changes course, water then moves in an opposite direction towards the northern side of Long Point.

In Haldimand, the Grand River has experienced ice jams in winter and early spring.  These ice jams dam up water upstream of them causing flooding in low-lying areas such as parts of Cayuga.


Health Impacts

The severity of damage caused by a flood depends on the depth, flow velocity, duration, contamination and sediment load, as well as the density and vulnerability of population, property and infrastructure.

Besides drowning, floodwaters can carry debris that can crush and injure people in the water.  Persons exposed to floodwater may also be prone to hypothermia.  Floodwater can contaminate drinking water and result in other hazardous exposures to people (e.g. infecting open wounds or being accidentally ingested).  Mold growth should also be considered in buildings that suffered water damage.  Additionally, standing water left over from floods can become breeding grounds for mosquitoes when temperatures are warm enough.


Other Impacts
  • Sewage systems may be overwhelmed and damaged by the excess water resulting in raw sewage backing up into buildings.
  • Electricity may be turned off to the affected areas in order to prevent accidental electrocution.
  • Water quality may diminish due to bacteria, sewage, or chemicals being introduced into the water supply by the flood.
  • Gas lines may be damaged or out of service.
  • Emergency response ground vehicles may be unable to respond if roads and bridges are flooded, washed out, or covered by debris.
  • The transportation of both people and goods may be halted if roads are flooded.
  • Support networks and healthcare services may be disrupted.


Before the Flood
  • Keep a 72-hour emergency kit ready to go.
  • Determine what you will do with your pets. Have them cared for by family, friends or kennel that is out of the flood zone until the situation is safe for their return. If you intend to bring them with you should flooding occur, have crates and leashes ready to go.
  • Put weather protection sealant around basement windows and the base of ground-level doors.
  • Install the drainage for downspouts a sufficient distance from your residence to ensure that water moves away from the building.
  • Consider installing a sump pump and zero reverse flow valves/ check valves in basement floor drains. Sump pumps should also be equipped with back-up battery power in case the hydro goes out.
  • Do not store your important documents in the basement. Keep them at a higher level, protected from flood damage.
  • Know how to turn off your gas, electricity and water. Keep instructions nearby.


If a Flood is Forecasted
  • Ensure vehicles are fueled and cell phones are charged.
  • Fill clean water containers.
  • Move essential items and household chemicals to an upper floor.
  • Bring in outdoor furniture (if you have enough time)
  • Turn off basement furnaces and the outside gas valve.
  • Take special precautions to safeguard electrical, natural gas or propane heating equipment. If there is enough time, consult your electricity or fuel supplier for instructions.
  • Shut off the electricity only if flooding has not yet begun and the area around the fuse box is completely dry. Stand to the side of the breaker panel and look away from the panel when switching the power off. Be sure to have a flashlight with you.


During the Flood
  • Stay informed. Listen to local radio and seek other credible sources of information (e.g. County website, media releases from authorities).
  • Determine where to go to stay safe and try to seek direction from authorities.
    • Evacuate if told to do so
    • Move to higher ground or a higher floor
    • Stay where you are if you cannot leave the area
  • Wear personal protective clothing and equipment when you encounter floodwater. This may include rubber boots (steel toed if possible) waterproof gloves, a facemask and eye protection (safety goggles). A floatation device is also recommended. Use a stick to check the ground in front of you.
  • Never enter a flooded area alone
  • Stay away from edges of waterways, as the banks can be slippery. Bridges over fast moving water should also be avoided.
  • Keep children away from floodwater. Stay within sight and arm’s reach of children when outdoors near water.
  • Keep pets on a leash. Do not try to rescue pets by going into cold or rushing floodwater.
  • Wash your hands often. Always wash your hands with soap and clean water or use an alcohol-based hand rub before preparing or eating food, after toilet use, after contact with floodwater, and after handling articles contaminated with floodwater.
  • If you rely on a private well or cistern for drinking water, do not use it for drinking, washing dishes, brushing teeth, preparing food, making ice or baby formula drink the water until you have determined if your water supply has been affected by floodwater. Water at or above your well head or cistern lid are a couple signs that your water supply may be contaminated.  Testing your well water should occur after the floodwaters have receded.  The HNHU offers free water sampling to test for bacteria.
  • If you cut or puncture your skin, clean and disinfect the wound as soon as possible. Try to keep the wound dry and clean.  Seek medical attention if you have not had a tetanus shot in the past 10 years or if the wound appears to be infected (e.g. redness, swelling infection, pus).
  • If you are on a private septic system, toilets should not be flushed and sinks should not be drained if your septic system is not submerged in floodwater. Using your septic system when it is submerged can result in sewage backing up into your home.


If Evacuating
  • Take your 72-hour emergency kit with you.
  • Follow the routes specified by officials. Don’t take shortcuts as they could lead you to a blocked or dangerous area.
  • Make arrangements for pets. Pets should be leashed or crated.  Bring pet food if you have time.
  • Time permitting, leave a note informing others when you left and where you went. If you have a mailbox, leave the note there.\


If Driving

The following are important points to remember when driving in flood conditions:

  • Do not attempt to drive through a flooded road. The depth of water is not always obvious. The roadbed may be washed out under the water, and you could be stranded or trapped.
  • Six inches of water can reach the bottom of some passenger cars causing loss of control and possible stalling.
  • Some vehicles may even float in 1 foot of water.
  • Two feet of rushing water can carry away most vehicles including sport utility vehicles (SUV’s) and pick-ups.
  • Do not drive around a barricade as they are there for your protection. Turn around and go the other way.
  • Do not try to take short cuts. They may be blocked. Stick to designated evacuation routes or directions given by authorities.
  • Be especially cautious driving at night when it is harder to recognize flood dangers.
  • If your vehicle becomes trapped in rapidly moving water, stay inside and unlock the doors. If water is rising in the vehicle, seek safety on the roof.


After the Flood
  • Do not return home until authorities have advised that it is safe to do so.
  • Wear appropriate protective equipment (e.g. rubber boots (steel toed if possible), gloves, N95 facemask and eye protection) when cleaning up.
  • If the main power switch was not turned off prior to flooding, do not re-enter your home until a qualified electrician has determined it is safe to do so.
  • Use extreme caution when returning to your home after a flood. Ensure the building is structurally safe prior to entering.
    • Look for buckled walls or floors.
    • Watch for holes in the floor, broken glass and other potentially dangerous debris.
  • If you smell gas or suspect a leak, turn off the main gas valve, open all windows and leave your house. Notify the gas company and police or fire departments.  Do not turn on lights or do anything that could cause a spark.
  • Do not touch electrical equipment if it is wet or if you are standing in water. Appliances that may have been flooded pose a risk of shock or fire when turned on. Do not use any appliances, heating, pressure, or sewage system until electrical components have been thoroughly cleaned, dried, and inspected by a qualified electrician.
  • The main electrical panel must be cleaned, dried, and tested by a qualified electrician to ensure that it is safe.
  • Do not use your private water supply for drinking, washing dishes, brushing teeth, preparing food, making ice or baby formula until it has been tested and deemed safe for use. For instructions on how to disinfect wells and cisterns, visit
  • Check on your septic system and monitor your property for signs of malfunction. Visible damage in or around the tank or tile bed as well as odours in the area or home and an unusual colour of ponding water could be signs of a malfunctioning septic system. Holding and septic tanks may continue to be pumped out as necessary, however, under flood-like conditions, caution should be taken to ensure the tank is not emptied too much, making it prone to float and break drain lines due to high groundwater levels.


Clean Up

Recommended equipment to clean up after a flood includes (but may not be limited to):

  • protective equipment (e.g. rubber boots (steel toed if possible), gloves, N95 facemask and eye protection)
  • pails, mops and squeegees
  • plastic garbage bags
  • unscented detergent
  • large containers for soaking bedding, clothing and linens, and clotheslines to hang them to dry
  • extension cords,
  • submersible pumps,
  • wet/dry shop vacuums,
  • carbon monoxide sensor
  • dehumidifiers, fans or heaters


Items to Discard

All of the following materials likely need to be discarded if exposed to floodwater:

  • insulation materials,
  • particleboard furniture,
  • mattresses and box springs,
  • stuffed toys,
  • pillows cushions
  • furniture coverings


Items that are Salvageable

All of the following materials may be salvageable if exposed to floodwater:

  • Frames of high-quality furniture can often be saved. They must first be cleaned, disinfected and rinsed, then dried by ventilation away from direct sunlight or heat. Drying too quickly can cause warping and cracking.
  • Clothes can be cleaned. Scrape heavy dirt from washable clothes. Rinse and wash them several times with detergent and dry quickly.
  • Drain floodwater from your home in stages—about one third of the volume daily. If the ground is still saturated and water is removed too quickly, the walls or the floor could buckle.
  • Use pumps or pails to remove standing water, then a wet/dry shop vacuum to mop up the rest.
  • Clear the yard of all debris and refuse as it can attract pests.
  • Do not heat your home to more than 4°C (about 40°F) until all of the water is removed.
  • If you use pumps or heaters powered by gasoline, kerosene or propane, buy and install a carbon monoxide sensor. Improperly ventilated combustion devices can result in carbon monoxide poisoning.
  • Whether you use a wood, gas or electrical heating system, have it thoroughly inspected by a qualified technician before use. Replace the furnace blower motor, switches and controls if they have been soaked.
  • Flooded forced-air heating ducts and return-duct pans should be either cleaned thoroughly or replaced.
  • Replace filters and insulation inside furnaces, water heaters, refrigerators and freezers if they have been wet. It may be cheaper to replace the entire appliance.
  • Remove all soaked and dirty materials as well as debris.
  • Break open walls and remove drywall, wood paneling and insulation at least 50 centimetres (20 inches) above the high-water line.
  • Wash of any dirt sticking to walls and solid-wood furniture then rinse several times.
  • Wash and wipe down all surfaces and structures with unscented detergent and water then rinse.
  • Flush and disinfect floor drains and sump pumps with detergent and water. Scrub them to remove greasy dirt and grime.
  • Clean or replace footing drains outside the foundation when they are clogged. Consult a professional for advice or service.
  • Ventilate or dehumidify the house until it is completely dry.
  • Rinse and then clean all floors as quickly as possible.
  • Replace flooring that has been deeply penetrated by floodwater or sewage.
  • Clean all interior walls and floor cavities with a solution of water and unscented detergent. Dry carpets within the first two days. For large areas, hire a qualified professional. Discard carpets soaked with sewage immediately.
  • To test if the material is dry, tape clear food wrap to the surface of the item. If the covered section turns darker than the surrounding material, it is still damp. Dry until this no longer occurs.
  • For upholstered furniture, consult a professional to see what can be salvaged. In the meantime, remove cushions and dry them separately. Do not remove upholstery. Raise furniture on blocks and place fans underneath.
  • Remove drawers and open doors of wooden furniture. Do not dry quickly or splitting may occur.
  • Ensure all contaminated dishes and utensils have been thoroughly washed and disinfected using safe, potable water (e.g. boiled or bottled water). Start by washing and rinsing contaminated dishes and utensils.  Then sanitize them in a solution of ½ to one teaspoon (2 to 5 mL) household bleach to 1 litre of water (or one to two tablespoons /½ – 1 ounce bleach to 1 gallon water).  Keep items soaking in solution for at least 45 seconds and let air dry.


  • Mold can lead to serious health problems to the occupants of formerly flooded buildings, even well after the flood occurred.
  • You may need to have your home professionally cleaned for it to be covered by insurance. Check with your insurance company. If your insurance company suggests you can clean it yourself, smaller patches of mould (one square-metre or less) can be removed by washing with soap and water and ensuring surfaces dry completely.  However, a professional should be consulted for larger mold damage.
  • If you are cleaning up in a room where mold is present wear an N95 face mask, goggles and disposable gloves.
  • To minimize mold growth, move items to a cool, dry area within 48 hours and set up fans.
  • Alternatively, textiles, furs, paper and books can be frozen until they are treated.
  • Wet mold will smear if wiped. Let it dry and then brush it off outdoors.


Food and Medicine
  • Undamaged canned goods must be thoroughly washed and disinfected.
  • Dispose of all medicines, cosmetics and other toiletries that have been exposed to flood water.
  • Dispose of any of the following food items if they have been exposed to flood water:
    • Contents of freezer or refrigerator, including all meats and all fresh fruit and vegetables
    • All boxed foods
    • All bottled drinks and products in jars, since the area under the seal of jars and bottles cannot be properly disinfected
    • Cans with large dents or that reveal seepage
  • If the flood resulted in a power outage, some perishable foods requiring refrigeration may have to be discarded. A refrigerator without power should keep food cool for about four to six hours if the door is kept closed. A full freezer without power will keep items frozen for about two days. A half-full freezer will keep items frozen for about one day. Meat, fish, poultry, eggs, soft cheeses, milk and leftovers should be thrown out if they have been at temperatures above 4°C for more than two hours.  For more information on food safety during a power outage, click here.
  • For more information on handling food after a flood, visit