# LA's Rainy Season and Your Sewer Lateral: What to Check Before Winter Storms | Angeleno Sewer Line Repair > Most of LA's rain falls from December to March. How storms affect a sewer lateral, why cracked pipes take in water and a short checklist for before winter. URL: https://lasewerlinerepair.com/blog/la-rainy-season-sewer-lateral-checklist/ ## LA's Rainy Season and Your Sewer Lateral Most of the year's rain arrives in four months. A few checks in the fall keep a weak lateral from becoming a winter backup. By Angeleno Sewer Line Repair · Updated October 20, 2026 Los Angeles gets most of its rain in a short window. NOAA’s 1991–2020 climate normals for the downtown station put average annual precipitation at 14.25 inches, and about 11.6 of those inches fall from December through March. October and November together average under an inch and a half. That makes fall the natural time to look at your sewer lateral, before the wettest months arrive. The sewer lateral is the private pipe from your house to the City’s main in the street. In Los Angeles, rain is supposed to go to the storm drain system, not the sanitary sewer. But a lateral is not a sealed tube once it is old or damaged, and wet weather exposes the weaknesses it already has. [Angeleno Sewer Line Repair](/) arranges inspections and repairs across Los Angeles, Pasadena, Glendale and Burbank, and here is what is worth checking before the storms. ### How rain gets into a sewer lateral Water reaches a lateral two ways. **Through the ground.** When soil around the pipe is saturated, water seeps in through open clay joints, cracks and broken sections. This is called infiltration. A sound pipe keeps it out; a damaged one lets it in, along with soil and sand that can settle in the line. A cracked lateral works in both directions: in dry months it can leak sewage out into the soil, and in wet months it can let groundwater in. **Through openings at the surface.** A cleanout with a missing or broken cap at ground level, especially one in a low spot in the yard, becomes a drain for surface water. So does any downspout or yard drain that was connected to the sewer at some point, which it should not be. We have not found local data that measures how much rainwater enters private laterals in Los Angeles, so we will not put a number on it. The mechanism is well established, though, and it explains why some lines that are slow all year become a problem after a big storm. ### Why storms can cause backups During heavy rain, extra water in the sewer system can raise the level in the main. A lateral that already has a partial blockage, such as a root mass, a grease buildup or a belly holding solids, has less capacity to begin with. Add more water and it backs up at the lowest drain in the house. This is also why the City requires a backwater valve on some properties. In the City of Los Angeles, a backwater valve is required when the lowest fixture in the building sits below the next upstream manhole cover, and installing one needs an LADBS plumbing permit. The valve lets flow out and closes against flow coming back. If you have a basement bathroom or a house set below the street, it is worth asking whether yours needs one. ### Roots do not take the winter off In much of the country, roots slow down in the cold. In Los Angeles they keep growing, because NOAA’s normals show essentially no frost days in the basin. Roots that entered an open joint during the dry season are still there when the rain arrives, catching debris as the flow increases. LA Sanitation attributes more than half of sewer backups to tree roots and grease combined. If your line has needed root clearing before, fall is a sensible time to have it done again, and to film it while it is clean. Cutting roots restores flow but does not seal the joint they came through, so they return. See [tree roots in sewer line](/tree-root-sewer-repair/) for the options. ### A short checklist before winter - **Find the cleanout and check the cap.** It should be intact and screwed down. A broken cap lets rain and debris in. If you have no cleanout, [adding one](/sewer-cleanout-installation/) makes future clearing faster. - **Look at where downspouts and yard drains go.** They should discharge to the yard, the street or a storm drain connection, never into a sewer cleanout. - **Notice last winter’s pattern.** If drains slowed or gurgled after storms, the line may have a defect that wet weather exposes. - **Watch for wet or sunken spots** along the line’s route during dry weeks, which can mean a leak. - **Clear known roots** before the wet months if the line has a history. - **Film the line** if it has backed up before, you have just bought the house, or you are not sure of its condition. A [sewer camera inspection](/sewer-camera-inspection/) shows open joints, cracks, roots and sags with the distance from the cleanout for each. In the City of Los Angeles, LA Sanitation offers a rebate of up to $300 toward a camera inspection, first come, first served while annual funds last. ### If a storm backup happens Stop using water, keep people away from the wastewater, and figure out whether the problem is yours or the City’s. If sewage is coming out of a manhole in the street, or several neighbors are backing up at once, call LA Sanitation’s 24-hour line at 1-800-773-2489. If only your house is affected, the lateral is the likely cause. Our guide on [what to do during a sewer backup](/guide/sewer-backup-what-to-do/) covers the first hour, and [signs of a broken sewer line](/guide/signs-of-a-broken-sewer-line/) helps sort a clog from a structural problem. A dry October is the easiest time to do any of this. The ground is firm, a trench stays open without fighting water, and the decision does not have to be made with sewage on the bathroom floor. Questions about your own sewer line? Phones answered 24/7, every day. [Call (213) 782-3753](tel:+12137823753)[Get an Estimate](/contact/) - [signs of a broken sewer line](/guide/signs-of-a-broken-sewer-line/) - [sewer backup what to do](/guide/sewer-backup-what-to-do/) - [sewer camera inspection](/sewer-camera-inspection/) - [sewer cleanout installation](/sewer-cleanout-installation/) - [tree root sewer repair](/tree-root-sewer-repair/)