Quick answer: When dirty water comes up through the shower or tub drain, especially when a toilet flushes or the washer drains, the blockage is almost always in the main line that carries everything out of the house. The shower is usually the lowest drain, so wastewater backs up there first. Stop using water, keep away from the dirty water, and call a plumber. Santa Cruz County Public Works names kitchen grease, flushed solids and tree roots as the common causes, and the property owner is responsible for the sewer lateral all the way to the public main.
Why the shower is where it shows up
Every drain in the house feeds into one main line. When that line is blocked, wastewater from the toilet, sinks, dishwasher or washing machine has nowhere to go and rises out of the lowest opening, which is usually a shower, tub or floor drain. A clog in the shower drain itself only slows the shower. Dirty water coming up from somewhere else points to the main line.
What to do right away
- Stop running water. No flushing, laundry, dishwasher or showers until the line is cleared.
- Keep people and pets away from the backed-up water, and wash your hands after any contact.
- Do not use chemical drain openers. They will not reach a main line blockage and make the job dangerous for whoever clears it.
- Find your cleanout. The county advises learning where the sewer lines and cleanouts are on your property. The City of Santa Cruz notes the lateral cleanout is usually in or near the sidewalk. A plumber clears the line through it.
- Call a plumber. A plumber can clear the line mechanically and, with a sewer camera inspection, see what caused it.
If sewage is flowing onto the street or into a storm drain, Santa Cruz County Public Works says to call 911.
Common causes of main line blockages
- Kitchen grease. The county calls it a leading cause of blockages in residential sewer lines. It cools and hardens inside the pipe.
- Flushed solids. Wipes, diapers, hygiene products and paper towels. Only human waste and toilet paper belong in the toilet.
- Tree roots. Roots grow into joints and cracks, as in the photo above, and catch everything that flows past.
- Broken, sagging or collapsed pipe. A low spot or break in an older line collects debris and keeps clogging.
Who is responsible for the sewer line?
Santa Cruz County Public Works says maintaining the residential sewer lateral is the property owner's responsibility, all the way to the connection with the main line. The City of Santa Cruz says the same for properties in the city, and holds owners liable for spills caused by a failed private lateral, with a fine for repeat spills.
How to prevent another backup
- Keep grease out of the sink. Let it cool and put it in the trash.
- Flush only toilet paper.
- Know where your cleanouts are.
- Santa Cruz County Public Works recommends having a plumber clear the lateral mechanically at least every 2 years.
- If roots or a damaged pipe caused the backup, a camera inspection shows whether the line needs repair.
On a septic property, a shower backup can also mean the tank or drain field is full or failing. See our guides to septic warning signs and slow drains.
Frequently asked questions
Why does water come up in my shower when I flush the toilet?
The toilet's water cannot get past a blockage in the main line, so it rises out of the lowest drain in the house, often the shower.
Can I clear a main line blockage myself?
A plunger or small hand snake will not reach a main line clog. It takes a sewer cable machine or hydro jetting through the cleanout.
How often should the sewer lateral be cleaned?
Santa Cruz County Public Works recommends mechanical clearing by a plumber at least every 2 years.
Sources
- Santa Cruz County Public Works, Preventing Sewer Overflows
- City of Santa Cruz Public Works, City Sanitary Sewer System
- U.S. EPA, How to Care for Your Septic System
Need help with a shower backup?
Wade's Plumbing & Septic provides drain cleaning, sewer camera inspection and septic inspections across Santa Cruz County and nearby Santa Clara County communities. Quotes are free and pricing is flat rate, quoted on site before work begins. Request service or call during office hours, Monday to Friday, 9:00 AM to 5:00 PM.
