Quick answer
Floodwater reaches home plumbing in four main ways: it can push sewage back through low drains, contaminate drinking water, soak water heaters and their controls, and sit in crawlspaces around pipes and insulation. Know where your main shutoff is, treat standing water as contaminated, limit drain use when sewers are full, and have flooded equipment inspected before restoring service.
What happened in December 2025
A series of atmospheric river storms hit Western Washington in early December 2025. On Wednesday, December 10, the Snohomish River rose about 10 feet in 24 hours, according to National Weather Service charts cited by the Snohomish County Tribune. On Thursday, December 11, it crested at 34.15 feet, about nine feet above major flood stage and above the previous record of 33.5 feet set in the 1990 flood.
In Snohomish County, floodwater covered downtown Sultan to a depth of a few feet. In the city of Snohomish, fire crews evacuated residents of homes on Lincoln Avenue before dawn on December 11. City emergency coordinator Shari Ireton said on December 12 that the city's wastewater treatment plant remained in good condition.
In Skagit County, KUOW reported on December 11 that about 100,000 people in the Skagit Valley were under evacuation orders. The Skagit River at Mount Vernon crested at a record 37.73 feet, and Cascadia Daily News reported that the downtown river wall held and that floodwater did not flow over it.
In Whatcom County, residents of Nooksack, Sumas and Everson were evacuated, and Cascadia Daily News reported that about 90 percent of Sumas residents left. Afterward, the recovery group Whatcom Strong coordinated volunteers who mucked out houses and cleaned crawl spaces to prevent mold. The area had flooded for the second time in four years.
Why floodwater becomes a plumbing problem
The Snohomish County Health Department warned after the event that floodwater can contain sewage, chemicals and mold, and advised people to treat all standing water as contaminated. Home plumbing is two systems: pressurized supply lines that bring clean water in, and gravity drains that carry wastewater out. High water affects both.
The drain side is the one most people do not think about. When the ground is saturated and nearby rivers and ditches are high, the sewer lines that drains connect to can fill and slow down. In a general plumbing sense, the first fixtures to show it are the lowest ones in the house: floor drains, basement toilets, shower pans and laundry sinks. This is a general principle of how drains work, not a finding from a report.
Warning signs include gurgling after a flush, several fixtures draining slowly at once, or water in the lowest drain in the house. If those signs appear during high water, reduce water use. Every flush and shower adds volume to a line that may have nowhere to send it.
Contaminated water and the main shutoff
Public health guidance from the Snohomish County Health Department said people on an affected water system should use bottled, treated or boiled water, and that water with an odd smell or discoloration should be boiled for a full minute before drinking. Public Health, Seattle and King County said much the same, specifying a rolling boil for one minute, and added that anyone re-entering a building with standing water should first turn off power, gas and water.
That last step depends on knowing where the main water shutoff is. A KATU report on winter pipe protection noted that the main shutoff is often in a basement, crawl space or garage, and may be indoors or outdoors. Every adult in the household should know where it is and how the valve turns.
The King County guidance also says not to touch electrical equipment while touching water and to call the utility for an emergency disconnect.
Water heaters and other equipment
Water heaters often sit in garages, basements and crawlspaces, which are the first places floodwater reaches. A flooded heater is not simply a wet appliance. Gas valves, burner controls, thermostats and electric elements are all components that were not designed to be submerged.
One published guide to flood-damaged heating equipment, from the reference site InspectApedia, advises that flooded safety and limit controls should be replaced rather than reused, and that a flooded electrical system should be left off until it has been inspected.
For gas-fired units, the gas supply is a matter for the gas utility or a licensed gas fitter. Anyone who smells gas should follow the Snohomish County Health Department guidance, which says to turn off gas, electricity or propane if a leak is suspected and to notify the gas company, police or fire department. A plumber can assess the water side of a heater, including connections, relief valve piping and the tank itself, once the energy source has been made safe.
Crawlspaces: where the water stays
Volunteers in Whatcom County cleaned crawl spaces specifically to prevent mold. Public Health, Seattle and King County says mold can start growing 24 to 48 hours after a flood, and the Snohomish County Health Department says it can begin forming within a day or two.
For plumbing, a flooded crawlspace matters for several reasons. Supply and drain lines run through it, and moving water can loosen their hangers and supports. Soaked insulation stops doing its job and holds moisture against pipes, which also leaves them more exposed in the next cold snap.
After the water is gone and it is safe to enter, look for sagging drain lines, disconnected joints, wet or missing insulation and any drip or damp spot along supply lines. A simple leak check helps: shut off every fixture, then watch the water meter or its low-flow indicator. If it keeps moving, water is going somewhere.
Wells and septic systems are separate work
Some homes are not on city sewer or a public water system. The Snohomish County Health Department advises well owners to use bottled, treated or boiled water and to disinfect wells after floodwaters recede. For septic systems, it advises stopping non-essential water use, avoiding the system if the drain field is underwater, and not pumping the tank while the ground is flooded because the tank could float out of the ground.
Wells, well pumps and septic systems are specialist work. Pyper does not service them. A licensed septic professional, a well contractor or the local health department is the right contact. Pyper's work starts on the house side, with the supply piping, drains, fixtures and water heater inside and around the building.
A practical sequence after the water recedes
This order draws on the guidance above and common plumbing practice. Local health department and utility instructions take priority.
- Stay out of any area with standing water and live electrical equipment until power is confirmed off.
- Close the main water shutoff if the building was flooded, and keep it closed until you know the supply lines are intact.
- Check local water system notices before drinking from the tap. Use bottled, treated or boiled water if told to.
- Reduce use of toilets, showers and washers if drains are slow or sewage is present at low fixtures.
- Do not restart a flooded water heater. Have the energy source made safe, then have the unit inspected.
- Photograph damage before cleanup, and report it through your county's damage survey if one is open.
- Once the building is safe, inspect crawlspace pipes, insulation and drain supports, and run a meter check for leaks.
When to call Pyper Plumbing
Some post-flood plumbing problems are urgent. Sewage or wastewater coming up through a floor drain or toilet, a supply line that was torn or loosened, a water heater that sat in floodwater, and a leak that shows on the meter all fall under emergency plumbing. Pyper provides emergency repair, leak detection and repair, water heater service, drain cleaning and sewer line repair in Snohomish, Skagit, Whatcom and Island counties.
If it is not an emergency, scheduling an inspection of crawlspace plumbing after the water is gone is reasonable. Gas lines, septic tanks and drain fields, and wells and well pumps are outside what Pyper does, so those problems should go to the right specialist.
Common questions
Can sewage back up into a house during river flooding?
It can. When the ground is saturated and sewer lines are full or slow, wastewater can come up through the lowest drains in a house, such as floor drains and basement fixtures. Reducing water use during high water and avoiding contact with any backed-up water are the first steps. Public health agencies advise treating floodwater as potentially containing sewage.
Is tap water safe to drink after a flood?
It depends on your water system. The Snohomish County Health Department advised people on an affected system to use bottled, treated or boiled water and to check with their water district for current conditions. Water that smells odd or looks discolored should be boiled for a full minute before drinking.
Should I turn the water heater back on after it was in floodwater?
No, not until the energy source is made safe and the unit is inspected. Controls, gas valves and electric elements are not designed to be submerged. For gas appliances, contact the gas utility or a licensed gas fitter. A plumber can then check the water-side connections and decide whether the tank can stay in service.
Sources
Facts in this guide come from the following references. Local rules and manufacturer instructions can differ, so follow your utility and your equipment manual.
- Snohomish River flood tops record level (Snohomish County Tribune)
- 100,000 evacuated in historic Skagit Valley flood (KUOW via Northwest Public Broadcasting)
- Thursday update: Skagit County under evacuation, Nooksack River at Cedarville crests (Cascadia Daily News)
- A tale of two cities: Mount Vernon, Sumas face very different recovery efforts after historic flooding (Cascadia Daily News)
- Health department issues safety guidance for flood clean-up (HeraldNet)
- Safety steps before entering a flooded building (Public Health Insider, Public Health - Seattle & King County)
- Protect your pipes: How to prepare your home for winter weather (KATU)
- How to clean and restart flooded heating equipment or restore a flooded water heater (InspectApedia)
This guide is general information, not a substitute for an on-site inspection. If you smell natural gas, leave the building and call 911 or your gas utility. Pyper does not perform gas line work.
