Preventing Sewer Backups During Heavy Rain

Why Rain Causes Sewer Backups

In many older municipalities, stormwater and sanitary sewer share the same pipes (combined sewer systems). During heavy rain, the massive volume of stormwater overwhelms the system capacity, causing sewage to back up through the lowest connections — typically basement floor drains and first-floor fixtures. Even homes on separate sewer systems can experience rain-related backups if cracks in the sewer lateral allow groundwater infiltration, or if the municipal system is overwhelmed and backs up into branch lines.

Installing a Backwater Valve

A backwater valve (also called a backflow preventer) is the most effective protection against sewer backups. This valve is installed on your main sewer lateral and allows sewage to flow out of your home normally but automatically closes if sewage attempts to flow backward into your home. Backwater valves can be installed inside (in a basement floor pit) or outside (in a yard access pit). Many cities offer rebate programs for homeowners who install backwater valves. Some insurance policies require them for sewer backup coverage.

Other Preventive Measures

Disconnect downspouts and sump pumps from the sanitary sewer if they are currently connected — this is often required by code and reduces the volume entering the system during storms. Ensure your foundation drainage and grading direct surface water away from the house. Seal basement floor cracks that could allow backed-up sewage to enter. Install a battery-backup sump pump to handle groundwater during power outages that often accompany severe storms. Keep your sewer lateral clean and free of roots that reduce capacity and increase the risk of backup during peak flow periods.

Emergency Response

If a sewer backup occurs, stop using all water fixtures immediately. If safe to do so, use sandbags or plugs to block floor drains. Avoid contact with sewage water, which contains harmful bacteria and viruses. Do not use electrical equipment in contact with standing sewage water. Once the backup subsides, document the damage with photos for insurance claims. Professional cleanup is recommended for sewage backups, as proper disinfection requires specialized equipment and cleaning agents. Most homeowner insurance policies do not cover sewer backup damage unless you have purchased a specific sewer backup rider.