What to Do When You Have Water in Your Basement After Heavy Rain
Finding water in your basement after heavy rain is one of the worst surprises a home can hand you. Maybe the sump pump was struggling, maybe you came down the stairs to a soaked carpet, or maybe the water is still rising while you read this. Whatever brought you here, take a breath. It is stressful, it is more common around Hamilton than most people think, and it can be handled safely if you take it in the right order.
Here is what this guide covers: what to do in the first few minutes, why basements flood after a storm, whether your furnace and water heater are safe to run again, and how to keep the next big rain from doing the same thing. Boonstra has been keeping Hamilton homes comfortable since 1961, and we work both sides of a flood like this: the licensed inspection of your heating and hot water equipment, and the plumbing that stops it happening again.
First steps if your basement is flooding right now
- Stay out of the standing water until the power is off. Do not go in if water is near outlets, baseboard heaters, the furnace, or the electrical panel.
- Shut off the power only if the panel is dry and you can reach it safely. If it is not, call your utility and have them disconnect it.
- Do not relight any gas appliance that has been in water. It needs a licensed inspection first.
- Take photos and video of everything before you move or clean anything.
- Once power and gas are confirmed safe, start removing the standing water and drying the space.
- Call your insurer, and call a 24/7 team to check the source and the equipment.
First, Stay Safe: What to Do Right Now
The instinct is to grab a bucket and start bailing. Hold off. The first few minutes are about safety, not cleanup, and floodwater plus electricity is the reason why.
Stay out of standing water until the power is off
The Electrical Safety Authority is blunt about this: water and electricity are a lethal mix. Electricity moves through water and wet flooring, and a shock can be serious. Do not step into the basement if the water is above your outlets, is touching baseboard heaters or the furnace, or is anywhere near the electrical panel. Standing water can be live even when nothing looks wrong.
Shut off the power only if the panel is dry and reachable
If your electrical panel is dry, easy to get to, and you can reach it without stepping in water, switch off the power. If any of that is in doubt, leave it alone and call your utility to disconnect power to the home. After a flood, have a Licensed Electrical Contractor check the system before power goes back on, and ask for an ESA Certificate of Acceptance for your records and your insurer.
Do not relight gas appliances, and leave if you smell gas
A gas appliance that has been sitting in floodwater is not safe to switch back on, full stop. A furnace, boiler, or water heater that has been in water may look fine and still be dangerous, and it needs a licensed inspection before it runs again. This is exactly the part Boonstra handles: call us at (289) 768-2332 and one of our licensed technicians will inspect your furnace, boiler, or water heater before it fires up. Do not relight anything yourself. If you smell gas, or you see a gas line that is broken or exposed, leave the home right away and call your gas company from somewhere safe.
Photograph everything, then call for help
Before you move a single box or run a fan, document the damage. Photos and video of the water line, the affected rooms, and your belongings. Insurers want proof before they approve a claim, and this is easy to capture now and impossible to recreate later. After that, the water still has to come out and the source still has to be found. A flooded basement is rarely a one-trade job, but we can help you navigate it and Boonstra answers 24/7.
Do and Don’t in the first hour
| Do | Don’t |
|---|---|
| Keep people and pets out of the standing water | Wade in for belongings before the power is off |
| Cut power at a dry, reachable panel, or call the utility | Touch a wet panel or a submerged outlet |
| Photograph all the damage before you clean up | Start hauling things out before you document |
| Get any flooded gas appliance inspected before it runs | Relight the furnace or water heater yourself |
| Wear rubber boots, gloves, and a mask near the water | Assume the water is clean |
Why Is My Basement Flooding After Heavy Rain?
Figuring out where the water is coming from tells you who can fix it and how to stop it from coming back. After a big storm around Hamilton, a handful of causes show up far more often than the rest.
Sewer backup and surcharge is the most common storm-driven cause here. When heavy rain overwhelms the municipal sewer, water rises above your basement floor and pushes back up through floor drains, toilets, or laundry connections. It is also the messiest, because that water is not clean.
A blocked or failed sewer lateral is a close second. The pipe that carries wastewater out to the municipal sewer can get choked by tree roots or break down with age. A camera inspection finds the blockage, which is drain work our plumbing team does.
Foundation cracks and seepage show up when saturated ground presses on the foundation and water works through cracks, gaps around pipes, and porous concrete.
A failed or overwhelmed sump pump is another regular offender. If it fails, loses power, or cannot keep up with the volume, the water it was holding back ends up on your floor.
Window wells, grading, and downspouts send water the wrong way, filling and leaking, sloping rain toward the walls, or dumping roof runoff against the foundation.
Where the water is coming in, and who fixes it
| Where you see the water | Most likely cause | Who fixes it |
|---|---|---|
| Up through floor drains or the toilet | Sewer backup or surcharge, or a blocked lateral | Boonstra plumbing and drain cleaning |
| Through foundation wall or floor cracks | Seepage under ground-water pressure | A waterproofing specialist |
| Around the sump pit, or the pump ran and quit | Failed, overwhelmed, or power-lost sump pump | Boonstra plumbing |
| Below a basement window | Leaking or overflowing window well | Waterproofing or grading specialist |
| A wall that is wet after every storm | Grading or downspouts sending water to the foundation | Exterior drainage or grading specialist |
Is Your Furnace or Water Heater Safe After a Flood?
This is the part most flood articles skip, and it is the part that matters most for your safety. A restoration crew dries the room. They do not inspect the gas-fired equipment sitting in the middle of it. Boonstra does, and after 60-plus years of Hamilton basements we know what floodwater does to it.
Do not restart a furnace that has been in floodwater. If your furnace sat in water, or water reached its base, leave it off. It can look perfectly fine and still be unsafe. Gas appliances in Ontario fall under the Technical Standards and Safety Authority, and only a licensed gas technician, G1 or G2, may work on the gas components. That unit needs a licensed inspection before it is powered or gassed back on, which is the kind of post-flood check our team does every storm season.
Why flooded equipment is dangerous: floodwater carries silt, sewage, and corrosive grit into the parts you cannot see. A submerged gas control valve can fail in the open position, so gas keeps flowing when it should stop. Silt and corrosion chew up burners, ignition controls, circuit boards, and safety sensors, and contaminated insulation cannot be cleaned, so it has to be replaced. A damaged valve, burner, or vent raises the risk of a gas leak and of carbon monoxide.
Safety note: Never try to restart, relight, or dry out flooded gas or electrical equipment yourself. A furnace, boiler, water heater, or air conditioner that has been in floodwater has to be inspected by a licensed technician before it is powered or gassed back on. There is no shortcut here, and no reason to gamble.
Water heaters are especially exposed. Once floodwater reaches the burner and controls of a gas water heater, the safe call is usually replacement rather than repair, because the controls and insulation that keep it safe cannot be reliably restored after being submerged.
Repair or replace? As a general industry standard, flooded water heaters, furnaces, cooling equipment, venting, and insulation are generally replaced rather than repaired. A licensed technician has to inspect any flooded furnace, boiler, water heater, or AC before it runs, and flooded gas-fired equipment is often a replacement, not a repair. A good technician will tell you which one you are looking at, and why, before anyone spends a dollar.
How to Stop It From Happening Again
Once the emergency is behind you, the goal is making the next big storm a non-event. The right combination depends on how the water got in, which is why the diagnostic above matters. This is where Boonstra’s plumbing team can help!
Sump pumps and battery backups. A sump pump is your frontline defence against groundwater, collecting it around your foundation and pumping it away before it reaches the floor. The catch: the storms that make a sump pump most necessary are the same ones most likely to cut your power, and a standard pump stops the second the power does. A battery backup keeps it running through an outage. Our plumbing team can help you with a backwater valve installation, or a sump pump installation.
Backwater (backflow) valves. A backwater valve sits on your sewer lateral and closes automatically when water tries to flow back toward the house. When the municipal sewer surcharges in a storm, the valve shuts and keeps sewage out of your basement. Since sewer backup is the most common storm cause here, this one addresses the problem at its source.
Sump pump vs backwater valve: what each protects against
| Sump pump | Backwater valve | |
|---|---|---|
| Protects against | Groundwater rising around the foundation | Sewage backing up from the municipal sewer |
| Where it sits | In a pit in your basement floor | On your sewer lateral |
| When it works | Continuously, as groundwater collects | Automatically, when the sewer surcharges |
| Needs power? | Yes (add a battery backup) | No, it is mechanical |
| Common failure | Power loss or volume overload | Debris holding the flap open (needs maintenance) |
They solve two different problems, which is why plenty of Hamilton homes end up with both. A sump pump handles groundwater. A backwater valve handles sewer backup. One is not a stand-in for the other.
Waterproofing, downspouts, and grading. If the water is coming through the foundation itself, that is a job for a waterproofing specialist. We don’t currently offer waterproofing but we can point you toward someone who does. Some of the most effective prevention is also the cheapest, and you can do a lot of it yourself: extend your downspouts so roof water discharges well away from the foundation, regrade soil that slopes toward the house, and keep your eavestroughs and drains clear. A maintenance plan keeps the small things from turning into the next flood.
Does Home Insurance Cover Basement Flooding in Ontario?
This is general information, not advice, and the only reliable answer comes from your own policy. That said, here is the part a lot of homeowners do not learn until it is too late.
A standard home insurance policy in Canada does not automatically cover basement flooding. According to the Insurance Bureau of Canada, the protection usually comes from two separate optional add-ons. Sewer backup coverage handles damage from sewer or septic backup. Overland water coverage handles surface water from heavy rain, overflowing rivers or lakes, and fast snowmelt. Both often carry limits, and overland coverage can be restricted in higher-risk areas.
The trap is assuming you are covered. Plenty of homeowners find out after a flood that they had neither add-on. It is worth a five-minute call to your insurer or broker to confirm what you actually have, before the next storm rather than after it. And whatever your coverage looks like, document the damage before you clean up. For context: water is now the leading cause of home insurance claims in Canada, ahead of both fire and theft, and severe weather is pushing that trend, with insured damage in 2025 among the highest years on record.
When to Call Boonstra
A flooded basement is one of those problems where the sooner someone looks at it, the less it costs. Water that sits keeps soaking into concrete, wood, and insulation, and mould gets going fast. If your basement has taken on water, have someone check both the source and your equipment.
A call makes sense when:
- Water reached your furnace, boiler, or water heater, and it needs a licensed inspection before anything runs again.
- Water is coming up through floor drains or the toilet, which points to sewer backup.
- The sump pump failed, ran dry, or could not keep up.
- You want to stop this from happening again with a backwater valve, a sump pump with a battery backup, or drain work.
Boonstra covers two big pieces of a flood like this on one call: the licensed inspection of your gas-fired heating and hot water equipment, and the plumbing that keeps the water out next time. For the electrical check and any foundation waterproofing, we will point you to the right licensed trades. We have been doing this across Hamilton and the surrounding area since 1961, and we answer 24/7.
Ready to get your basement sorted?
A flooded basement is a bad day. Getting it checked, dried, and protected against the next storm is how you keep it a one-time thing.
Call the Boonstra team and we will handle our side of it: the licensed inspection of your furnace, boiler, and water heater, and the plumbing that keeps water out next time. Same rate at 2 AM as 2 PM. No overtime charge, and the same steady help whenever you need it.
Or call us anytime: (289) 768-2332
The pros in the green trucks at Boonstra have been serving Hamilton, Ancaster, Dundas, Stoney Creek, Waterdown, Burlington, and the surrounding area since 1961. Available 24/7.
Frequently Asked Questions About Flooded Basements in Hamilton
Why does my basement flood when it rains heavily?
Around Hamilton, the most common cause is sewer backup, when heavy rain overwhelms the municipal sewer and water pushes up through your floor drains. Other frequent causes are foundation cracks and seepage, a failed or overwhelmed sump pump, and grading or downspouts sending rainwater toward your foundation.
What should I do first if my basement is flooding?
Stay out of the standing water until the power is off, because water and electricity are a dangerous mix. Shut the power off only if the panel is dry and reachable, otherwise call your utility. Do not relight gas appliances, photograph the damage, then call a 24/7 team.
Is it safe to use my furnace after it has been in a flood?
No, not until a licensed technician inspects it. Floodwater damages gas valves, burners, controls, and insulation in ways you cannot see, which raises the risk of a gas leak or carbon monoxide. A submerged furnace is often a replacement rather than a repair. Never restart it yourself.
Do I need a sump pump and a backwater valve, or just one?
They guard against different problems, so many homes need both. A sump pump moves groundwater away from your foundation. A backwater valve stops sewage backing up out of the municipal sewer during a storm. One does not replace the other, so the right answer depends on how water is getting in.
Does home insurance cover basement flooding in Ontario?
Usually not automatically. A standard policy typically excludes it, and coverage comes from two optional add-ons: sewer backup and overland water. They cover different causes, both often carry limits, and many homeowners find out after a flood that they had neither. Check your own policy with your insurer or broker.
Is standing water in a flooded basement dangerous?
Yes, for two reasons. It can be electrically charged if it reaches outlets, wiring, or the panel, so stay out until the power is off. It can also carry sewage, chemicals, and pathogens, especially in a sewer backup. Keep contact to a minimum, and wear rubber boots, gloves, and a mask during cleanup.
How soon should I call a professional after a basement flood?
As soon as the immediate hazards are handled. The longer water sits, the deeper it soaks into concrete, wood, and insulation, and the faster mould grows. A quick check of both the water source and any flooded gas equipment limits the damage and keeps your home safe. Boonstra answers 24/7.