Sewage or drain water is backing up. Treat it as a health problem.

Stop using water anywhere in the building, including the washing machine and the dishwasher, and keep people and pets out of the affected area. Every fixture you run sends more water at a blockage that is already backing up into the house.

This is not a spill to mop. Water that has come back up out of a drain is contaminated, and the way it is handled is different from every other kind of water damage on this site.

Why running water makes it worse

A backup means the line leaving your house is blocked or overwhelmed. Anything you send down a drain has to go somewhere, and if it cannot leave, it comes up at the lowest opening in the building. That is usually a basement floor drain, a shower on the lowest floor, or a ground floor toilet.

So the first instruction is negative. Do not flush, do not shower, do not start a load of laundry, and tell everyone else in the building the same thing.

Work out how far the blockage is

The pattern of which fixtures are affected tells you where the problem sits, and that decides who fixes it.

One fixture only, everything else fine: a local blockage. A single blocked toilet or a blocked kitchen drain. Deal with it as a fixture blockage.

Several fixtures on the lowest floor, or a floor drain flooding: the blockage is in the main line leaving the house. Everything upstream backs up into the lowest opening. This is a plumber, and often a drain specialist with a camera.

Every drain in the building, and the neighbors have it too, or it happened during heavy rain: the problem is likely on the municipal side or the system is overwhelmed by storm water. Call the water or sewer authority. Most run a 24 hour line, most will come out, and if the blockage is on their side the work is usually theirs to do.

A septic system: a backup usually means the tank is full, the drain field has failed, or the line to the tank is blocked. Stop using water entirely and call a septic contractor. Continuing to use water with a full tank pushes the problem back into the house. What has usually gone wrong, and what the contractor should do.

What to do while you wait

• Keep the area sealed off. Close the door, and put a towel at the bottom of it to stop the water tracking into the next room.
• Lift anything you want to keep off the floor in adjoining rooms.
• Switch off the circuit serving the affected area if the panel is dry and you can reach it safely.
• Open a window in that room if the weather allows, and keep the door to the rest of the house closed. You want that air going outside, not through the building.
• Do not run a fan or a dehumidifier in contaminated water. Air movement across it aerosolizes what is in it and moves it through the house.
• Photograph everything from the doorway before anyone touches it.

That last point matters more here than anywhere else, because the cleanup will involve throwing things away, and by the time an adjuster looks at it the evidence will be at the curb.

Is the house safe to stay in?

That depends on how far it spread, whether it reached the furnace or any ductwork, and whether anyone living there is pregnant, elderly, very young, or immune compromised. The three questions, and what makes a house uninhabitable.

Why this one is not a do it yourself job

With clean water, the answer is usually to dry it fast and keep the material. With category three water, the answer is that porous material which absorbed it does not get saved:

• Carpet and carpet pad come out.
• Drywall is cut out above the water line, usually well above it, because it wicks.
• Insulation in a wet wall cavity comes out.
• Particleboard, chipboard, and anything laminated onto it comes out.
• Upholstered furniture and mattresses that absorbed it come out.

Hard, non porous surfaces such as concrete, tile, and sealed metal can be cleaned and disinfected. Everything else is a judgment about how much absorbed how much, and it is made in favor of removal. The full list of what goes and what stays, and where the boundary is for cleaning it yourself.

The other reason is what the drying equipment does. Running air movers over contaminated material before it is removed and the area is cleaned distributes that contamination through the house, which is a bigger problem than the wet basement you started with.

The insurance point, and it is a trap

A sewer or drain backup is very often not covered by a standard homeowners policy. Most policies exclude water that backs up through sewers or drains, or that overflows from a sump, unless you have bought a specific endorsement for it, usually called water backup or sewer backup coverage.

That endorsement is inexpensive relative to what a backed up basement costs, and it is usually sold with a modest limit, so it is worth knowing your number now rather than during a claim. What the endorsement does and where it gets argued.

Two things follow from that:

• Call your insurer early and ask specifically whether you carry water backup coverage, before you commit to a restoration contract. Late notice is one of the most common reasons claims get denied.
• If the backup was caused by a failure on the municipal side, the sewer authority may have its own claims process. It is separate from your insurance and it usually has a short deadline.

If it happened because the system was overwhelmed by heavy rain rather than by a blockage, the flood exclusion may also be in play, which is a different argument again.

Before anyone starts work

Ask the contractor two questions. What category are they treating the water as, and what are they removing rather than drying. If the answers are category three and a removal list, that matches the standard. If someone proposes to dry sewage water in place and save the carpet, get another opinion.

Get the scope in writing before work starts, and understand what you are signing. An assignment of benefits hands your rights under the policy to the contractor, and it is worth reading before you sign it rather than after.

The short version

Stop using water. Stay out of it. Do not clean it, do not dry it in place, and do not run a fan over it. Work out from which fixtures are affected whether it is local, in your main line, or the municipality’s. Check whether you carry water backup coverage before you agree to anything.