Electrical safety, stopping water use, and bringing in a verified RBQ-licenced contractor.
Safety first: contaminated water and electricity
A sewer backup brings back to the surface what the pipe was supposed to carry away: water loaded with bacteria and organic matter. Treat any risen water as potentially unsanitary: avoid skin contact, wear boots and gloves if you absolutely must cross the area, and wash thoroughly after any exposure.
Electricity is the second major risk. If water is approaching outlets, appliances or the electrical panel, switch off the affected zone’s breaker, but only from a dry spot, never wading through water to reach the panel. Neither plug in nor use any electrical device inside the flooded area.
Ventilate if possible and keep children and pets away. Above all, resist the reflex to clean everything immediately: the priorities are stopping further inflow and documenting: deep cleaning comes after the intervention.
Stopping the water feeding the problem
During a backup, every litre you send into the network risks returning through the lowest point. So stop all water consumption immediately: toilets, faucets, showers, washer and dishwasher included. Close the washer and dishwasher valves if needed so a cycle cannot start unnoticed.
Warn everyone in the home (family, roommates, neighbours in a small multi-unit building), that the network is off-limits until the professional has ruled. In multi-unit buildings, a basement backup potentially involves the whole stack: quick coordination avoids nasty surprises.
Note the context: did the backup follow heavy rain, spring melt, or is it happening in dry weather? Those details strongly steer the diagnosis (internal clog, overloaded line, or a problem further downstream), and speed up the professional’s assessment on arrival.
Document, then bring in a verified RBQ-licenced contractor
Before any intervention, photograph the extent of the water, the backup points and affected belongings. Those images support your insurance claim and provide a factual baseline for diagnosis: notably to distinguish an internal clog from an event affecting the municipal line.
Then call a verified RBQ-licenced contractor: they will identify the real cause (internal line clog, roots, damaged section), clear it or steer you toward appropriate work, and can document findings with a camera inspection. Depending on the cause and the problem’s exact location, responsibility may lie with the owner or the municipality: the professional diagnosis exists precisely to establish that.
As a reference point, an unclogging intervention with camera inspection generally sits within an indicative range of $220 to $1,800 depending on complexity: an indicative range to be confirmed on site. Nordis matches you quickly with a vetted professional covering your area.
Verified and sourced
Verified on September 27, 2026
Official sources
What these numbers do not cover
Emergency steps limit the damage but do not fix the cause; no amount is quoted here.