A sewer backup after rain in Los Angeles almost always means the line was already in trouble before the storm. LA keeps rainwater and sewage in separate pipes, so rain only reaches your sewer through cracks, separated joints, root holes, or a drain that was never supposed to be tied in. Roots are the usual cause. LA Sanitation reports that more than 50% of sewer backups come from tree roots and grease.
The call usually comes in the morning after the first real storm of the season. The shower drain in the back bathroom is gurgling. The toilet won’t go down. There’s gray water around the tub drain that wasn’t there last night. And the part every homeowner mentions is that it’s been fine all summer.
That’s exactly the problem. Here’s why the first storm finds the weak spot, how to tell whether it’s your line or the city’s, and what to do before the next one.
Why Rain Gets Into a Sewer Line That Isn’t Built for It
Rain gets into a sewer line in two ways: through connections that shouldn’t exist, and through pipe that isn’t sealed anymore. Your sewer lateral (the pipe that runs from your house to the city main under the street) is sized for what comes out of your sinks, tubs and toilets. It was never meant to carry a roof’s worth of rain.
The first way is a direct connection. Older homes and weekend projects sometimes tie a downspout, a patio drain or a yard drain straight into the sewer clean-out. In a storm that pipe fills with rainwater on top of the household flow. LA County Public Works is blunt about it. Keep rainwater out of the sewer, because it overwhelms the lines and can cause spills.
The second way is slower and harder to see. Much of LA County’s older housing has clay or cast-iron laterals, and clay pipe comes in short sections with a joint every few feet. When those joints crack or pull apart, soaked soil around the pipe drains straight into it. So does groundwater. The line ends up carrying the house plus the yard.
Most homes here don’t have basements, so the water shows up at the lowest opening on the line. That’s usually a ground-floor shower or tub, a back bathroom toilet, or the clean-out in the yard.
Why Sewer Backup After Rain Is Worst in the First Storm
The first storm of the season is the worst because roots have had all summer to grow into the pipe. Most of LA’s rain falls between December and March. From late spring through fall, the soil around your lateral dries out, and the steadiest source of moisture underground is the vapor escaping from a sewer joint.
Roots find it. A root hair slips through a hairline gap at the joint, then thickens inside the pipe into a mat that catches toilet paper and grease. A USDA Forest Service review of root intrusion found roots are reported to cause more than half of all sewer blockages, and that older pipe with joints, shallow pipe and small-diameter pipe are the most vulnerable. That describes most residential laterals in older LA neighborhoods.
All summer, a half-blocked line still keeps up with a household. Water trickles past the roots and nobody notices. Then the storm adds rainwater from a connected downspout and seepage from wet soil, the flow jumps, and the roots act like a dam. The water backs up to the lowest drain in the house.
So the storm didn’t break anything. It just showed you what the roots had been doing since April.
Is It Your Sewer Line or the City’s?
In most of Los Angeles County, the whole lateral is yours, including the part under the sidewalk and street. The City of Los Angeles says property owners are responsible for the private lateral from the building all the way to the street connection, and LA County Public Works says the same for the sewers it maintains. The city owns the main.
A few quick checks tell you which side of that line the problem is on:
- Ask a neighbor or two. If several houses on the street are backing up at once, the city main may be surcharged. Call your city’s sewer maintenance line.
- Notice which drain goes first. Water rising in the lowest shower or tub while upstairs fixtures still drain points to your main line, not one clogged fixture.
- Listen when the washer drains. A toilet that gurgles or bubbles when the washing machine empties means the main line is partly blocked.
- Check the timing. Problems that start during rain and ease a day after are classic root and infiltration behavior.
If it’s your lateral, the next step is a camera inspection and sewer line service so you’re fixing the actual defect instead of guessing.
Buying an older home in LA? Ask for a sewer camera inspection before you close. Root-choked clay laterals are common, and once escrow closes, the lateral is yours to fix.
What You Can Check Before the Next Storm
You can do a lot of the detective work yourself, and none of it requires opening the pipe.
Start by finding your clean-out. It’s usually a capped 3 or 4 inch pipe sticking out of the ground near the foundation or along the path toward the street. Knowing where it is saves time when a plumber arrives. Then walk the house in the rain or right after. Follow every downspout and yard drain and see where it goes. If one disappears into the clean-out or into the ground near the sewer line, it may be tied into the sewer, and it should be rerouted to the yard or the storm drain.
Two things not to do. Don’t pour chemical drain opener or root killer into a line that’s already backed up, because it sits in the pipe and burns whoever opens it next. And don’t unscrew the clean-out cap while the line is backed up. The line is under pressure, and the sewage comes out fast.
If water is coming up right now, stop running water in the house, keep kids and pets away from it, and call for 24/7 emergency plumbing help.
How a Line That Backs Up in the Rain Gets Fixed
We camera the line first. Every time. The video shows where the roots are, whether the joints are just leaking or actually separated, and whether there’s a sag or a crack. We record it and walk you through it before anyone quotes a repair, because the right fix depends entirely on what’s in the pipe.
| What the camera shows | The usual fix | What to expect |
|---|---|---|
| Roots at a few joints, pipe otherwise sound | Hydro jetting to clear the full pipe diameter | Roots regrow through the same joints, so plan on regular cleaning |
| One or two joints separated or cracked | Spot repair of the failed section | Removes the entry point; the rest of the line keeps working |
| Many failing joints, offsets or a collapse | Lateral replacement, trenchless where digging is a bad idea | New pipe with sealed or fused joints, so roots have no easy way in |
| House drains sit below the street manhole | Backwater valve on the house line | Protects against city-side surges, not against your own clog |
Honestly, a lot of lines just need cleaning. If the pipe is sound and the roots are light, jetting is the cheaper answer, and the same USDA review notes that small pipes with roots commonly need clearing every year or two. It depends on how bad the joints are. Once a joint has separated, roots come back faster every season, and repairing that section usually costs less over time than paying to clear it again and again.
The backwater valve matters for houses that sit low. Under California Plumbing Code section 710.1, fixtures on a floor lower than the next upstream manhole cover have to be protected by an approved backwater valve. Hillside and low-lot homes are where we see this most.
Tree-Lined Streets in Burbank and Pasadena
The neighborhoods people love for their trees are the ones that see this most every November. In older Pasadena neighborhoods, a century-old street canopy sits over original clay laterals, and roots find every joint.
Burbank has a rule worth knowing before any digging starts. If a City-owned parkway tree crushes or displaces your sewer lateral, the city may reimburse the repair of that portion under Resolution No. 17,805. But a City inspector has to see the damaged pipe before it’s removed, and the city’s sewer lateral specifications say photographs won’t be accepted instead. So for Burbank homes with a crushed section under a city tree, the pipe gets exposed and inspected first, then replaced. In another city, ask public works before the dig. Some cities have a program. Many don’t.
Get the Line Looked At Before the Rain
A sewer line that backed up in last year’s first storm will usually do it again this year, and a little worse. The best time to find out what’s in the pipe is a dry week in October or November, not a wet night in January.
Hard Hat Rooter and Plumbing runs camera inspections and hydro jetting across Los Angeles County from our shop in Burbank, 24 hours a day. You get a flat-rate price before any work starts. Call (855) 331-7788, and check our current coupons before you book.
