Sewer backups and stormwater floods: how to tell them apart

Water inside a home, business, or public area can come from several infrastructure problems. Two events that are often confused are a sanitary sewer backup and a stormwater flood. They may occur during the same heavy rain, but they involve different systems, hazards, and responses.

A sewer backup happens when wastewater cannot move through the sanitary sewer network and reverses direction into a building or property. A stormwater flood occurs when rain, snowmelt, or runoff exceeds the capacity of streets, drainage channels, inlets, pipes, or nearby waterways.

Knowing the source of the water helps residents protect their health, avoid property damage, and report the problem to the right municipal service. The Public Works resources available through the City of Susanville can help residents find information about utilities, streets, stormwater, emergencies, and related infrastructure.

What each event means

Sanitary sewers carry wastewater from toilets, sinks, showers, appliances, and commercial facilities to treatment infrastructure. A backup can develop when a sewer main is blocked, a private lateral is damaged, tree roots enter a pipe, or unusually high flows overwhelm the system. A failed sump pump or clogged building drain can create a similar indoor problem without a public sewer failure.

Stormwater systems handle runoff rather than household wastewater. Rain and melting snow travel across roofs, yards, driveways, streets, and other surfaces before entering storm drains, ditches, culverts, detention areas, or natural channels. Flooding may occur when an inlet is blocked, drainage infrastructure is undersized, frozen ground prevents absorption, or runoff arrives faster than the system can carry it away.

Where the water appears

A sanitary sewer problem often begins at a low drain inside the building. Water may rise through a toilet, floor drain, bathtub, shower, or cleanout. Multiple fixtures draining slowly at the same time can indicate a blockage in the building sewer or a nearby public main. The water may be gray or dark and may contain paper, solids, or a strong sewage odor.

Stormwater generally enters from outside. It can flow through a garage door, basement window, foundation crack, low doorway, or damaged wall. Floodwater may cover roads, collect in intersections, cross sidewalks, or enter yards from higher ground. It can look muddy or carry leaves, sediment, oil, trash, and other materials picked up from outdoor surfaces.

The distinction is not always obvious. A rainstorm can increase flows in a sanitary sewer through infiltration and illegal connections, while a storm drain can back up and push contaminated street water onto private property. The apparent entry point and the quality of the water are useful clues, but professional assessment may be needed.

Health and property risks

Sewage contains microorganisms and other contaminants that can cause illness. Anyone who comes into contact with backup water should avoid touching their face, wash thoroughly, and keep children and pets away. Porous materials such as carpeting, upholstered furniture, drywall, and insulation may need specialized cleaning or removal.

Stormwater is not automatically clean. Runoff can contain bacteria, animal waste, pesticides, metals, fuel, and other pollutants. Floodwater may also conceal sharp objects, open utility covers, unstable pavement, and electrical hazards. Never drive through moving or deep water when the depth and road condition are uncertain.

Feature	Sewer backup	Stormwater flood
Main source	Sanitary sewer, building drain, or private lateral	Rainfall, snowmelt, runoff, or drainage system
Common entry point	Toilets, floor drains, tubs, showers, or cleanouts	Doors, windows, foundations, streets, yards, and low areas
Typical appearance	Cloudy or dark water with sewage odor and solid waste	Muddy or clear runoff carrying leaves, sediment, oil, or debris
Primary concern	Pathogens and contaminated indoor surfaces	Flood exposure, pollutants, erosion, traffic, and electrical hazards
First response	Stop using plumbing and report a possible sewer issue	Stay clear of moving water and report blocked or overwhelmed drainage
Likely responsible area	Private plumbing, sewer lateral, or sanitary sewer main	Private drainage, storm drains, streets, channels, or culverts

What to do when water appears

If wastewater is rising indoors, stop using toilets, sinks, showers, washing machines, and dishwashers. Keep people and pets away from the affected area. If it is safe to do so, turn off electricity to wet areas from a dry location, but do not enter standing water to reach a panel. Contact a licensed plumber for a private blockage and notify the city if the problem may involve a public sewer main.

For outdoor flooding, avoid walking or driving through flowing water. Move vehicles and belongings only if doing so does not require entering an unsafe area. Keep storm drains and culverts clear from a safe position, but do not remove heavy debris or enter channels during active rainfall. Report blocked inlets, damaged drainage structures, flooded roads, or sinkholes through the appropriate city contact.

Photographs can document the location, water level, damaged infrastructure, and timing of the event. Do not handle contaminated materials without suitable protective equipment, and contact your insurer or a qualified cleanup contractor when interior flooding has occurred.

How to prevent repeat problems

Property owners can reduce sewer backup risk by keeping grease, wipes, paper towels, and unsuitable materials out of drains. A plumber can inspect a private sewer lateral, identify root intrusion, and recommend a backwater valve where appropriate. Backwater valves require maintenance and should be installed and serviced according to local requirements.

Stormwater protection starts with keeping roof gutters, downspouts, swales, driveway drains, and private inlets free of leaves and sediment. Direct downspouts away from foundations without sending concentrated flow onto neighboring property. During winter, avoid piling snow where melting water will run toward a building entrance or block a drain.

The City’s utility and infrastructure information can clarify responsibilities for public streets, drainage facilities, sewer service, and permits. Residents should also follow local conservation, construction, and safety guidance when making drainage improvements.

Practical steps before the next storm

• Locate household shutoff valves, electrical panels, floor drains, and exterior cleanouts.
• Keep a list of emergency contacts for the city, a plumber, an insurer, and cleanup services.
• Store important documents and valuable items above likely flood levels.
• Inspect gutters, private drains, sewer cleanouts, and sump pumps before wet weather.
• Teach household members to recognize sewage contamination and moving-water hazards.

A sewer backup and a stormwater flood require different diagnoses, even when both follow a major storm. Identifying where the water came from, avoiding exposure, and reporting damaged public infrastructure promptly can limit health risks and reduce damage.

Use the City of Susanville Public Works website to review current utility information, emergency contacts, project updates, and service guidance. Report urgent hazards as soon as it is safe, and arrange qualified inspection and cleanup before returning a contaminated area to normal use.