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A power outage during a basement flood creates a specific and dangerous combination: the sump stops working exactly when it is needed, and the electrical status of the room becomes uncertain rather than simply off.
Assume circuits will re-energise
This is the single most important point on this page. Power being out is not power being off. Utility supply returns without warning, and it returns to circuits that may be underwater.
If a generator is connected, the risk is worse rather than better. An improperly connected generator can backfeed circuits that appear dead, and it does so silently.
Treat every circuit in a wet basement as potentially live until the panel has been shut off from a dry location or a professional has confirmed otherwise. If reaching the panel means crossing water, that is a call to the utility or an electrician.
Why the sump stops
Most sump pumps are mains-powered with no reserve. A storm that causes a power failure is usually the same storm producing the groundwater the pump exists to handle, so the failure and the demand arrive together.
When the pump stops, the pit fills, and water then rises through the cove joint and the slab. This is a predictable failure mode with a well-understood fix — a battery backup pump, or a water-powered backup where the plumbing supports it — and it is the highest-value prevention measure for any basement that relies on a sump.
Do not run a generator or fuel pump indoors
Carbon monoxide is odourless and accumulates quickly in an enclosed basement. Generators and fuel-powered pumps run outdoors, well away from windows, doors, and intakes, without exception.
The same applies to any temporary heating. Unvented combustion in a closed basement is a serious risk independent of the water.
What you can do while the power is out
- Stay upstairs if water is rising, if utilities are wet, or if you cannot confirm electrical status.
- Shut off the main breaker only from a dry position outside the wet area.
- Photograph what you can see from the stairs with a torch. Documentation still counts.
- Move anything valuable and portable from the floor above the basement, in case humidity migrates upward.
- Do not use extension cords through wet areas, and do not plug anything in downstairs.
If water is rising and there is no safe way to slow it, the correct response is to leave it and call. A basement can be dried. Electrical injury cannot be undone.
When power returns
Do not simply switch appliances back on. A furnace, water heater, or freezer that has been partly submerged needs inspection before use — controls, gas valves, and motors are not designed to be wet, and failures can be delayed rather than immediate.
The sump may restart and run continuously. That is normal after an outage, but a pump that runs without lowering the pit level suggests a failed impeller, a stuck check valve, or a frozen or blocked discharge line.
Related pages
For entry decisions, see is it safe to go down there. For storm-driven flooding generally, see flooding during a storm. For prevention including sump backup, see cost, insurance, and prevention.