Note to readers: This post was updated on July 09, 2026 with current guidance on storm-season backups and links to our sewer line and emergency service guides. We refreshed the details below so the advice reflects how we approach this work today.
When heavy rain hits Southern California, drains that were already running slow can turn into full-blown backups fast. Storm runoff overwhelms a sewer line that already has roots, grease, or buildup narrowing it, and water that used to drain slowly now has nowhere to go. That’s when a nuisance clog becomes a flooded garage, laundry room, or backyard.
Why Rainy Season Makes Slow Drains Worse
Your main sewer line handles wastewater from your house and, in some cases, extra groundwater that seeps in through cracked or aging pipe. A line that’s 70% blocked might drain fine on a dry day but back up completely once rain adds volume. The pipe doesn’t fail overnight — it’s usually been narrowing for months from grease, soap scum, or tree roots working their way into the line.
Warning Signs Before the Storm
- Gurgling sounds from toilets or drains when you run water elsewhere in the house
- Slow drainage in multiple fixtures at once (not just one sink)
- Sewer odor near floor drains or cleanouts
- Water backing up into a tub or shower when the washing machine drains
Any of these mean your main line needs attention before the next storm, not after.
What to Do If You’re Already Flooding
Shut off water use in the house if you can — every flush and load of laundry adds more water with nowhere to go. Move anything valuable off the floor in the affected area. Then call a plumber who can get a sewer camera or jetter on-site. Trying to plunge or chemically treat a main line backup during an active flood rarely helps and can make a mess worse.
For a deeper look at what actually qualifies as an emergency versus something that can wait, see our guide on what counts as a real plumbing emergency.
Preventing It Next Time
The most reliable fix is getting your main line cleaned before rainy season, not during it. A camera inspection shows exactly what’s narrowing the pipe, and a professional cleaning — whether that’s hydro jetting or snaking, depending on the buildup — clears it out. If your home floods during storms every year, that’s a sign of a structural issue worth a full evaluation rather than a repeat emergency call.
Western Rooter & Plumbing runs 24/7 emergency service throughout the San Gabriel Valley for exactly these situations. If your drains are already showing warning signs, don’t wait for the next storm to find out how bad it is.
