Why Your Sewer Backs Up After Heavy Rain

San Antonio gets heavy downpours, and a sewer line that drains fine most of the year can back up during one. Here's why, and what to check.

Why rain causes backups

• Rainwater and groundwater seep into old, cracked sewer pipe and fill it.
• Wet clay soil swells and shifts buried pipe.
• A line already narrowed by roots or scale has less room for extra water.

What to check

• Your cleanout: water standing in it points to a main line problem.
• Downspouts: make sure they drain onto the ground, away from the cleanout.
• Which drains back up: the lowest drain in the house usually goes first.

After the storm

If backups only happen in heavy rain, ask for a camera inspection once the line is clear. Cracks that let water in also let roots in, and fixing them can stop both problems.

Why does my sewer back up only when it rains?

Rainwater can seep into cracked pipe and overload the line, especially if roots or scale have already narrowed it.