Winter Rain and Drain Backups

Groundwater rises and soil saturates in winter. Water seeps into cracked laterals and open joints, a process called infiltration. That extra water fills the pipe and leaves less room for wastewater from the house.

Over a dry summer, roots grow toward any moisture they can find, including small leaks in a lateral. When rain comes, those roots are already inside, and the extra flow pushes paper and debris into them.

If gutters, downspouts or yard drains are tied into the sewer lateral, they add storm water directly to it. Most cities, including those on the Peninsula, discourage these connections. Redirecting them to the surface reduces the load.

Gurgling toilets, slow tubs, water at the cleanout, or a smell after heavy rain. If these happen only during storms, the lateral may be partly blocked or cracked.

Have a slow lateral cleaned in the fall. Check that the cleanout cap is intact and visible. Disconnect any downspouts tied to the sewer. If you have had storm backups before, consider a video inspection.

If drains slow, cut water use. Avoid running the washer and dishwasher. If water rises in a tub or shower, stop using water and call a provider.

A backup during a storm can mean the system was overwhelmed or that your lateral has a problem. A video tells you which. See main sewer line cleaning and lateral inspection.

Many homeowners policies need a sewer backup endorsement. Check yours before storm season.

The first heavy rain after a long dry season often brings the most backup calls. Debris and roots that built up over summer meet a sudden rush of water. Having the lateral checked in early fall avoids that first-storm surprise.

Rain that enters cracked laterals adds to the flow in the city's mains. That is one reason cities on the Peninsula inspect laterals at point of sale: fixing private leaks helps the whole system during storms.

Homes that sit below the street or near the bottom of a slope can see backups when the system is under stress. A backwater valve and a clear lateral reduce the risk.

Note the date, the rain and what happened. A pattern over a few winters helps you and your provider decide what protection makes sense.

A local provider can clear the line, check it on video and suggest protection that fits your home.

Some Bay Area winters bring long bands of heavy rain over several days. Those storms saturate the ground and push the most water into cracked laterals and old joints. If a storm like that is forecast and your lateral has been slow, cleaning it beforehand is a smart move.

Street storm drains carry rainwater, usually toward the bay. Sanitary sewers carry wastewater to treatment. They are separate systems in most of the Peninsula, which is why rain entering a sanitary lateral is a problem the city tries to reduce.

Clean a slow lateral, check the cleanout cap, disconnect downspouts from the sewer, clear gutters and confirm your insurance covers sewer backups. Those five steps take little time and prevent most winter surprises.

A cracked or missing cleanout cap lets rain pour straight into the lateral. Check the cap each fall and replace it if it is damaged. It is one of the cheapest fixes there is.

If backups happen only in the heaviest storms, the lateral may be cracked and taking on groundwater. If they happen in every storm, it may also be partly blocked. A video helps sort out which.

Prepare in fall, cut water use during storms, and check the lateral after any backup.

A provider can clean a slow lateral before storm season or clear a backup during one. Calls to (650) 360-4973 are answered 24 hours a day by independent local providers, who explain the likely cause and how the price is set before any work starts. You decide whether to go ahead.

Walk the yard over the lateral and look for soggy patches, dips or a smell. Check the cleanout for standing water. Any of these after heavy rain is a reason to have the line looked at before the next storm.

Winter rain tests every weak spot in a lateral. A little preparation in the fall goes a long way. If a drain is backing up now, call (650) 360-4973 to reach a local San Bruno provider.