Sewer backup: what to do, and how to stop it happening again

What to do first

• Stop all water use. The City of Wentzville, Missouri advises not running water down drains until the blockage is cleared – every flush adds to what comes up.
• Watch for electricity. Be careful entering a flooded basement because of shock risk and contact with pollutants, Wentzville warns. Do not stand in water near outlets or appliances.
• Keep people out. The CDC advises keeping children and pets out of the area until cleanup is finished.
• Call a plumber who does drain and sewer work, and your city sewer utility if neighbors have the same problem.

Is it your line or the city’s?

Wentzville’s rule of thumb: if the backup happens only when you use water and slowly drains when you stop, the problem is most likely in your own sewer lateral – the pipe from the house to the public main. The City of Fargo lists warning signs of a sewer line blockage: several fixtures backing up at once, or one fixture backing up when another is used. Who pays depends on the city. Many make the property owner responsible for the whole line to the public main, as Fargo does; in Los Altos, California, the city handles the part past the property line. Ask your sewer utility.

Cleaning up safely

The EPA says raw sewage carries bacteria, viruses, parasites and molds, so treat any backup as a health hazard, and a basement flooded by sewage must be thoroughly cleaned and disinfected. The CDC advises rubber boots, rubber gloves and goggles, and for disaster cleanup recommends a solution of 1 cup of household bleach to 1 gallon of water – never mixed with other cleaners. Carpets, padding, upholstered furniture, mattresses and wallboard that sewage touched usually have to be thrown away, according to EPA and CDC. Large backups are often a job for a professional cleanup company.

Preventing the next one

• Backwater valve. A backwater valve closes when sewage tries to flow back into the house, as Gresham, Oregon explains. FEMA recommends having a licensed plumber install one.
• Disconnect downspouts. FEMA notes that downspouts connected to the sewer line can overload sewers in heavy rain and contribute to basement backups.
• Watch what goes down. Grease, wipes and food scraps build clogs – see our clogged drain guide.
• Camera inspection. If backups recur, a plumber can run a camera through the line to look for roots, sags or breaks.

A note on insurance

Standard policies treat sewer backup differently. Under the National Flood Insurance Program, flood insurance covers sewer backup damage only if it directly results from flooding, according to FEMA’s FloodSmart. Many homeowners policies need a separate sewer or water backup endorsement. Ask your insurer before you need it.