If your basement floor drain backing up when it rains, the water coming up through the drain is usually caused by an overwhelmed sewer system, a blocked main sewer line, or a failed sump pump. This is not a problem you can ignore. Standing water in your basement poses health risks, damages your belongings, and can weaken your home's foundation.
For homeowners in Spokane, this problem is especially common because parts of the city still rely on combined sewer systems that carry both sewage and stormwater in the same pipe. When heavy rain hits, those pipes fill up fast, and the overflow has to go somewhere. According to the U.S. Environmental Protection Agency, about 700 municipalities across the country still use combined sewer systems that can overflow during wet weather events.
Why Is Water Coming Up from Your Basement Drain?
When water rises through your basement floor drain after a storm, it means the water in the drainpipe has nowhere else to go. The basement floor drain is the lowest point in your plumbing system, so it is the first place where backed-up water shows itself. Understanding why water is coming up from your basement drain starts with understanding how your home connects to the city sewer.
How Your Basement Drain Connects to the Sewer
Your basement floor drain connects to a drain pipe that runs under the basement floor. That pipe joins the main sewer lateral, which is the pipe that carries wastewater from your home out to the city sewer main in the street. In normal conditions, water flows in one direction: away from your home. But when the city sewer main fills up during heavy rain, water pressure builds in the system. That pressure pushes water backward through the sewer lateral and into your home through the lowest drain, which is usually the basement floor drain.
Some homes also have a sump pump pit in the basement. The sump pump collects groundwater that seeps in around the foundation and pumps it outside. If the sump pump fails during a storm, groundwater rises, contributing to flooding. A working sump pump is your first line of defense against basement flooding during heavy rain.
Combined Sewer Systems and Rain Overload
Many older cities, including parts of Spokane, have combined sewer systems. These systems use a single pipe to carry both household wastewater and stormwater. In dry weather, the system handles the flow without problems. But during heavy rain, the volume of stormwater entering the system can overwhelm the pipes. When the system reaches capacity, the combined mix of stormwater and sewage backs up into homes through basement floor drains.
According to the City of Spokane, the city spent approximately $50 million in the 1980s to separate storm and sanitary sewers in most of north Spokane. However, some areas, including parts of the South Hill and older downtown neighborhoods, still use combined sewer systems. The city has built underground storage tanks to hold overflow during storms, but even with them, extremely heavy rainfall can still overwhelm the system and cause backups into homes.
Common Basement Drain Backup Causes
Basement drain backup causes fall into a few categories. Some are problems with the city sewer system, some are issues with your own plumbing, and some are related to conditions around your property. Knowing which category your problem falls into helps you find the right fix.
- City Sewer System Overload
When the municipal sewer system takes on more water than it can handle, pressure builds in the main sewer line under the street. That pressure forces water backward through the sewer lateral and into your home. This is the most common reason basements flood during heavy storms. The U.S. Environmental Protection Agency estimates that between 23,000 and 75,000 sanitary sewer overflows occur every year in the United States, and many more happen during major rain events through combined sewer systems. If your basement only floods during heavy rain and never at other times, a sewer system overload is the most likely cause.
- Blocked or Damaged Sewer Lateral
The sewer lateral is the pipe that runs from your home to the city sewer main. If this pipe is partially blocked by tree roots, grease buildup, or collapsed sections, it cannot handle the extra water flow during a storm. Even a partial blockage that does not cause problems in dry weather can create a full backup when rainwater adds to the volume. According to the U.S. Census Bureau, the median year of construction for homes in Spokane is 1961. Many of these older homes have clay or cast iron sewer laterals that are prone to cracking and root intrusion after decades of use.
A professional sewer camera inspection can show exactly what is happening inside the pipe. The camera reveals cracks, root intrusion, bellied sections where the pipe has sagged, and areas of heavy buildup. This inspection is one of the fastest ways to find the cause of a basement drain backup.
- Sump Pump Failure
If your home has a sump pump and the pump fails during a storm, groundwater that normally gets pumped out of the basement will rise and flood the floor. Power outages during storms are a common cause of sump pump failure. The pump cannot run without electricity unless it has a battery backup system. Mechanical failure, a stuck float switch, or a clogged intake are other reasons a sump pump can stop working when you need it most.
Homes in low-lying areas of Spokane, including parts of Spokane Valley and near the Spokane River, are especially at risk of sump pump failure during heavy rain. A sump pump service visit from a licensed plumber can test your pump, clean the pit, and make sure the system is ready before the next storm hits.
- Poor Yard Grading and Foundation Drainage
The slope of the ground around your home affects how much water reaches your foundation. If the yard slopes toward the house instead of away from it, rainwater pools around the foundation walls and seeps into the basement. Clogged or missing gutters and downspouts that dump water right next to the foundation make this worse. Over time, the soil around the foundation can settle, creating low spots that direct water toward the house instead of away from it.
How to Fix Basement Floor Drain Backup
If you are looking for how to fix a basement floor drain backup, the right solution depends on what is causing the problem. Some fixes are simple and affordable. Others require professional plumbing work. Here are the most effective options.
- Install a Backwater Valve
A backwater valve, also called a backflow preventer, is a device installed on your sewer lateral that allows wastewater to flow out of your home but prevents it from flowing back in. When the city sewer system backs up during a storm, the valve closes automatically, preventing sewage from entering your basement. This is one of the most effective long-term solutions for homes that experience repeated basement flooding during rain events.
A licensed plumber can install a backwater valve on your main sewer line, typically near where the pipe exits your home. The valve needs to be accessible for future maintenance and inspection. A professional backflow preventer installation gives you peace of mind that your home is protected every time it rains.
- Maintain or Upgrade Your Sump Pump
If your home has a sump pump, test it regularly to make sure it turns on when the water level rises. Pour a bucket of water into the sump pit and watch to see if the pump activates and drains the water. If it does not, the float switch may be stuck or the pump may need to be replaced. Most sump pumps last 7 to 10 years before needing replacement.
Adding a battery backup sump pump is one of the smartest upgrades you can make. Battery backup pumps kick in automatically when the power goes out, keeping your basement dry during the exact conditions when flooding is most likely. For homes that do not have a sump pump, installing one can prevent thousands of dollars in water damage over the life of the system.
- Clear the Main Sewer Line
If a blockage in your sewer lateral is making the backup worse during rain, clearing the line can make a big difference. Tree roots, grease buildup, and sediment all narrow the pipe and reduce its ability to handle extra water flow during storms. A professional drain cleaning service can remove these blockages using drain snaking or hydro jetting.
Hydro jetting is especially effective for sewer laterals because it cleans the full diameter of the pipe, not just the center. This restores the pipe to near-original capacity and gives it the best chance of handling storm water volume without backing up. If the pipe is cracked or collapsed, a sewer line repair may be needed to fully resolve the problem.
Floor Drain Backing Up in Basement: Immediate Steps
When you discover a floor drain backing up in your basement, acting quickly can limit the damage. Here is what to do in the first few minutes and hours after a backup.
Safety First
Before you enter the flooded area, check for electrical hazards. If water is near any outlets, appliances, or your electrical panel, do not step into the water. Turn off the power to the basement at the main breaker if you can do so safely. If you cannot reach the breaker without entering the water, call your utility company or an electrician.
If the backup water is dark, has a foul smell, or contains visible waste, it is likely sewage-contaminated. The Centers for Disease Control and Prevention warns that sewage backup water can contain harmful bacteria, viruses, and other pathogens that cause illness. Do not touch the water with bare skin. Wear rubber boots, waterproof gloves, and eye protection if you need to enter the area. Keep children and pets away from the flooded space.
Stop the Water and Start Cleanup
If a sump pump failure caused the flooding, check whether restoring power or resetting the pump will start draining the water. If the backup is from the sewer, you will need to wait until the storm subsides and the city sewer system drains down before the water in your basement recedes.
Once the water level drops, begin cleanup as soon as possible. Remove standing water with a wet-dry vacuum or pump. Open windows and run fans or dehumidifiers to start drying the space. Remove any wet carpeting, insulation, or drywall that was soaked with sewage water. These materials cannot be safely cleaned and must be thrown away. Disinfect all hard surfaces that contacted the water using a solution of one cup of bleach per gallon of water.
Health and Insurance Risks If Basement Flooding from the Drain
Basement flooding from a drain backup is more than just a mess. It creates real health hazards and financial problems that homeowners need to understand.
Health Risks of Sewage Backup
When a combined sewer system backs up into your home, the water is not clean rainwater. It is a mix of stormwater and raw sewage that may contain E. coli, salmonella, hepatitis A, and other harmful pathogens. The Centers for Disease Control and Prevention identifies sewage exposure as a source of gastrointestinal illness, skin infections, and respiratory problems, especially if mold begins to grow in the damp environment after the flooding.
Mold can start growing within 24 to 48 hours in a warm, damp basement. Airborne mold spores can trigger allergic reactions and respiratory problems even in people who were not directly exposed to the floodwater. Fast cleanup and thorough drying are essential to prevent mold from taking hold.
Insurance Coverage for Sewer Backups
Most standard homeowner insurance policies do not cover damage from sewer backups or sump pump failures. According to the Insurance Information Institute, water damage is the second most common type of homeowner insurance claim in the United States. However, sewer backup coverage is typically sold as a separate add-on, often called a water backup endorsement. This endorsement usually costs $50 to $250 per year and provides coverage of $5,000 to $25,000.
If you live in an area with a history of basement flooding, adding water backup coverage to your policy is a smart investment. Without it, you could be responsible for all the costs of cleanup, repairs, and replacement of damaged belongings. Talk to your insurance agent about your specific risks and coverage options.
Preventing Basement Floor Drain Backup in Spokane
Prevention is always cheaper and easier than dealing with the aftermath of a flood. Here are the most effective steps Spokane homeowners can take to prevent basement floor drain backups during rain events.
- Maintain Your Sewer Line
Schedule a professional sewer camera inspection every one to two years to check for tree roots, buildup, and pipe damage. If the inspection reveals a partial blockage, have it cleared before the next rainy season. Annual sewer line maintenance is especially important for older homes in Spokane, where decades of hard water mineral deposits and tree root growth can significantly reduce pipe capacity.
- Test and Maintain Your Sump Pump
Test your sump pump at least twice a year by pouring water into the pit and watching the pump activate. Clean the pit of any debris and check the discharge line for blockages. Replace the pump if it is more than 7 to 10 years old or if it struggles to keep up during storms. Consider installing a battery backup pump to protect against power outages.
- Improve Your Yard Drainage
The ground around your home should slope away from the foundation at a rate of at least six inches over the first 10 feet. This directs rainwater away from the house. Make sure gutters are clean and that downspouts extend at least 4 to 6 feet from the foundation. Fix any low spots in the yard where water pools after a storm. These simple grading improvements can dramatically reduce the amount of water that reaches your basement.
Prevention Checklist for Spokane Homeowners
Use this checklist to keep your basement dry during Spokane's rainy season and spring snowmelt:
- Schedule an annual sewer camera inspection to check for tree roots, grease, and pipe damage
- Test your sump pump twice a year and clean the pit of debris
- Install a battery backup sump pump to protect against power outages during storms
- Have a backwater valve installed on your sewer lateral to block sewage from flowing back into your home
- Keep gutters clean and make sure downspouts direct water at least four to six feet from the foundation
- Check that the ground around your home slopes away from the foundation
- Do not pour grease, wipes, or other clog-causing materials down any drain in your home
Why Basement Drain Backups Are Common in Spokane
Several local factors make Spokane homeowners more likely to experience basement drain backups during rain events than homeowners in many other cities.
Combined Sewer Systems in Older Neighborhoods
Spokane's sewer system dates back to the late 1800s. While the city has spent decades separating storm and sanitary sewers, some neighborhoods still have combined systems. According to the City of Spokane, the city has reduced combined sewer overflow volume by 86 percent through $50 million in sewer separation work, but the remaining combined sewer areas are in locations that are difficult to separate. Neighborhoods on the South Hill and in the older downtown core are among the areas most affected by combined sewer overflow during heavy storms.
Spokane's Climate and Seasonal Flooding Risk
Spokane averages about 16.5 inches of annual precipitation and 44 to 48 inches of snowfall each year, according to the City of Spokane's climate data. The highest risk of basement flooding occurs during two periods: late fall and early winter, when heavy rain events occur, and late winter through early spring, when snowmelt combines with rain. The soil around your foundation may already be saturated from months of winter moisture, so even a moderate rain event can push water into your basement during these times.
Sudden summer thunderstorms can also cause problems. While Spokane's summers are generally dry, an intense storm can dump heavy rain in a short time. If the sewer system or your property's drainage cannot handle the sudden volume, the result can be a backup in the basement floor drain.
Aging Home Infrastructure
According to the U.S. Census Bureau, the median year of construction for homes in Spokane is 1961, and about 25 percent of the housing stock was built before the 1940s. Older homes are more likely to have clay or cast iron sewer laterals that crack, corrode, or sag over time. They are also more likely to have inadequate drainage systems that were designed for the standards of a different era. Tree roots from decades of growth can infiltrate these aging pipes, creating blockages that get worse during every heavy rain.
When to Call a Professional Plumber in Spokane
Some basement floor drain backups are simple enough to handle on your own with basic cleanup. But there are clear signs that you need a professional plumber to diagnose and fix the underlying cause:
- Your basement drain backs up every time it rains, even during moderate storms, which points to a sewer line problem or a missing backwater valve
- You see sewage or dark water coming up through the drain, not just clear water, which means the main sewer line is involved
- Your sump pump runs constantly during rain or does not turn on at all
- Multiple drains in your home back up at the same time, indicating a main line blockage
- You smell sewage in your basement even when it is not raining, which can mean a cracked or broken sewer pipe
Our licensed plumbers at Mr. Rooter Plumbing of Spokane can diagnose the cause of your basement drain backup with a video camera inspection and recommend the right fix. Whether you need a backwater valve, sump pump repair, sewer line cleaning, or a full pipe replacement, our team has the tools and training to get the job done right.
Protect Your Spokane Basement Before the Next Storm
A basement floor drain that backs up after rain is telling you something important about your plumbing system. Whether the cause is a combined sewer overflow, a blocked sewer lateral, a failed sump pump, or poor yard drainage, the problem will only get worse with each storm. The cost of prevention is always less than the cost of cleanup and repair after a flood.
Spokane's aging sewer infrastructure, hard water, older homes, and seasonal weather patterns make basement drain backups a real risk for homeowners across the city. Do not wait for the next heavy rain to find out if your basement is protected. Contact Mr. Rooter Plumbing of Spokane to schedule a sewer line inspection and take the steps you need to keep your basement dry all year.
