How rain gets into a sewer line
Short answer: water soaks into the ground around your lateral and seeps in through cracks, open joints and root holes. The extra water fills the pipe, and whatever the pipe can’t carry comes back up through the lowest drain in the house.
A healthy lateral is sealed, so groundwater stays outside. An old clay or cast iron lateral usually isn’t. Clay joints open up as roots push between them, and cast iron cracks as it scales and thins. Each opening lets in more water during a storm.
Downspouts or yard drains tied into the sewer make it worse. Those connections send roof and yard runoff straight into a pipe that was never sized for it.
What to do during a backup
- Stop running water, flushing toilets and using the washing machine.
- Keep people and pets away from any sewage, and don’t touch it without gloves.
- If sewage is coming out of a manhole or into the street, call the city, since the main may be overloaded.
- If it’s only inside your house or at your cleanout, call a plumber to clear the line.
- Take photos for your insurer before you clean up.
Signs your lateral is letting water in
- Drains slow down or gurgle only when it’s raining
- The cleanout overflows during storms but not in dry weather
- A plumber has found roots in the line before
- The house was built before 1960 and the lateral has never been replaced
Finding the cause
Clearing the line gets the water moving again, but it doesn’t close the cracks. A camera inspection shows where water and roots are getting in and how much of the line is affected. In Whittier, the city asks for that video before it issues a lateral repair permit, so the inspection is the natural next step either way.
Stopping it from happening again
- Disconnect any downspouts or yard drains that tie into the sewer, and send that water to the yard or the street as your city allows.
- Have roots cleared before the rains start, rather than after the first backup.
- Repair or line the damaged sections the camera finds.
- Ask about a backwater valve if the house sits low compared with the street.
- If the lateral is failing along its whole length, plan a replacement for the dry months.
Clearing roots is not the same as clearing a blockage. A cable cuts a channel through the mass, while hydro jetting the line scours the pipe wall completely. That difference is why jetting usually buys another season before the roots return. Neither approach helps if the pipe itself has deteriorated, and replacing a failed lateral becomes the only permanent answer.
Age is the first thing to establish. Whittier’s older clay laterals separate at the joints, and a line installed before 1960 is generally near the end of its service life even where it has never backed up. Book the camera inspection in September, not January.