Flooded basement and sewer backup
Keeping groundwater and sewer water out of the basement, and the pumps, alarms and valves that do it.
How to keep a basement dry
Water gets into a basement two ways. Groundwater rises into the sump pit, and a sump pump sends it out. Sewer water comes up through floor drains and toilets, and only a backwater valve on the drain line stops it; many homes need both (Government of Canada).
Pump the groundwater out
A sump pump empties the pit before water reaches the floor. You can swap a pump like for like; a new pit is a job for a licensed plumbing contractor.
Plan for the pump stopping
Storms often bring power cuts just when the pump is needed, so add a backup and test it. A water-powered backup needs city water and a backflow preventer, and some cities ban them.
Stop sewer backup at the drain
A backwater valve on each basement drain, fitted by a licensed plumber, keeps sewage from coming up. Some cities require them and help pay, usually only if you are approved before the work starts.
Safety: If water is in the basement, never try to shut off the power with water present. Stay out until a qualified electrician says it is safe, and call your electricity utility or 911. Treat sewer water as contaminated. The Government of Canada’s flood advice and Health Canada’s clean-up guidance cover the rest.
What helps
A main pump, a backup for when it stops, an alarm that warns you, and a pump to clear the floor if water gets in anyway.
Sump pumps
Zoeller M98 Flow-Mate 1/2 HP Cast-Iron Sump Pump
Cast-iron 1/2 HP pump: 61 GPM at 10 ft for pits that fill fast
Zoeller Model 42 Floor Sucker 1/6 HP Portable Utility Pump
Pumps a flat floor down to 1/8 in through a garden hose
Backup pumps
Zoeller Aquanot Spin 508 12 V Battery Backup Sump Pump System
Self-testing 12 V backup rated on a real battery
Basepump HB1000-PRO Water-Powered Backup Sump Pump
No battery: runs on city water pressure for as long as it lasts
Water alarms
Basement Watchdog Water Alarm BWD-HWA
Loud 110 dB alarm; sensor wire reaches into the sump
YoLink Water Leak Sensor 4 Starter Kit
Four app-connected leak sensors with a freeze warning
$72.99–$89.99at YoLink (YoSmart) · prices may have changedPrice checked . Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on YoLink (YoSmart) at the time of purchase will apply to the purchase of this product.Check price at YoLink (YoSmart) (opens in a new tab)
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Guides
How-to
Basement flooded? What to do first
Power and safety first, then sewage or clean water, photos for your insurer, slow pumping and drying within 48 hours, in the order official guidance gives.
Best-of
The best battery backup sump pumps
Four backup sump pumps compared on the makers' own figures: flow at 10 ft, run time per battery, pit size and alarms that work offline.
Comparison
Battery vs water-powered backup sump pumps
Battery backups pump harder and work in any home; water-powered ones run through long outages but need city pressure, a backflow preventer and your town's approval.
Explainer
Backwater valves around Montréal: rules and subsidies
What Montréal, Laval, Longueuil and Pointe-Claire require for backwater valves, and what RénoPlex and PC-3002 pay towards them.
Questions about basement flooding
Does a sump pump stop sewer backup?
No. A sump pump removes groundwater from the pit. Sewer water coming up through floor drains and toilets is stopped by a backwater valve on the drain line, fitted by a plumber, as the Government of Canada’s flood advice explains. Many homes need both.
Battery or water-powered backup?
A battery backup works anywhere but runs for a limited time. A water-powered backup runs as long as city water pressure holds, but it needs municipal water, uses mains water to pump and needs a backflow preventer to protect the drinking water. Some cities ban water-powered backup pumps, so ask your municipality first.
Can I get help paying for a backwater valve?
Sometimes. Some cities subsidise backwater valves and sump pits, usually only if you are approved before the work starts, so ask your city first. Our backwater valve guide shows how one region’s rules and grants work.
Can I replace a sump pump myself?
Swapping a like-for-like pump in an existing pit is a simpler job; follow the pump maker’s instructions. A new pit or any change to the drains is work for a licensed plumbing contractor; ask for proof the work meets code with the invoice.
Do I need a water alarm if I have a backup pump?
Yes, as the early warning. A loud battery water alarm by the pit or drain sounds with no Wi-Fi needed, so you hear about water before it spreads, as our flooded basement guide suggests.
Comes with
Flooding
Keeping water out of the basement, a pump running when it rises, and what to do first if it gets in.
Power outages
Keeping the furnace, fridge and sump pump running when the grid goes down, and connecting backup power safely.