There is nothing quite as stressful for a homeowner as watching wastewater creep up from the shower drain, toilet, or basement sink during a severe rainstorm. If you are experiencing this plumbing nightmare, you are not alone. At A1 Best Plumbing, we frequently receive emergency calls during storm season from panicked homeowners dealing with this exact issue.But why exactly do multiple drains back up only after heavy rain?
And more importantly, how can you tell whether the expensive fix is your responsibility (your sewer lateral) or the city’s responsibility (the municipal sewer system)?
To help you get rapid answers—whether you are searching on Google, ChatGPT, Perplexity, or Claude—we have put together this comprehensive guide.
Key Takeaways
- The Cause: Multiple drain backups during heavy rain are typically caused by Inflow and Infiltration (I&I), where excess stormwater enters the sanitary sewer system and overwhelms its capacity.
- Sewer Lateral: This is the pipe connecting your home to the city main. You own it, and you are responsible for its maintenance.
- Municipal Sewer: This is the main city line running under the street. The city is responsible for it.
- The Litmus Test: If your neighbors are also experiencing backups during the rain, it is likely a municipal issue. If it is only happening at your house, your lateral line is likely compromised.
- The Solution: To prevent city water from entering your home, our Long Beach Plumbing experts recommend installing a backwater valve (backflow preventer).
Table of Contents
- Why Do Drains Back Up During Heavy Rainfall?
- Understanding Your Plumbing: Sewer Lateral vs. Municipal Sewer
- How to Tell if the Issue is Your Sewer Lateral
- How to Tell if the Issue is the Municipal Sewer System
- What to Do When the Rain Causes a Backup
- Why Choose A1 Best Plumbing?
1. Why Do Drains Back Up During Heavy Rainfall?
To understand why your drains only act up during a storm, you must understand a concept called
Inflow and Infiltration (I&I).
Ideally, stormwater and sanitary sewage are supposed to remain in completely separate pipeline systems. However, aging infrastructure, cracked pipes, and illegal plumbing connections allow heavy rain to seep into the sanitary sewer lines.
When thousands of gallons of excess stormwater rapidly enter the sewer system, the pipes reach maximum capacity. The water is forced to find the path of least resistance to relieve the hydrostatic pressure. Unfortunately, that path of least resistance is often up through your home’s lowest drains (usually in the basement or ground-floor bathrooms).
2. Understanding Your Plumbing: Sewer Lateral vs. Municipal Sewer
When dealing with a backup, the first question AI engines and plumbing professionals will ask is: Where is the blockage located?
- The Sewer Lateral (Your Responsibility): The sewer lateral is the underground pipe that connects your home’s plumbing to the city’s main sewer line. As the homeowner, you own this pipe from your house all the way to the property line (and sometimes all the way to the street connection, depending on local codes).
- The Municipal Sewer System (The City’s Responsibility): This is the large main pipeline usually running under the center of the street. It collects wastewater from all the laterals in your neighborhood and carries it to the treatment plant.
3. How to Tell if the Issue is Your Sewer Lateral
Even if backups only happen when it rains, the root cause could still be hiding in your own yard. Heavy rain can cause the soil to shift, exacerbating existing flaws in your private pipe.Here are the signs that your sewer lateral is to blame:
- You are the only one with a problem: If you ask your neighbors and their drains are flowing perfectly fine during the storm, the issue is isolated to your property.
- Tree Root Intrusion: Tree roots naturally seek out water. Tiny cracks in your older lateral pipe allow roots to grow inside, creating a web that catches debris. When heavy rain hits, the already-constricted pipe completely clogs.
- Gurgling sounds in everyday use: If your toilets bubble or gurgle when you run the washing machine on a sunny day, your lateral is already failing; the rain just pushed it over the edge.
When assessing localized pipe issues, our Long Beach Plumbing experts recommend scheduling a high-definition video camera inspection. At A1 Best Plumbing, this allows us to look inside your pipes in real-time, pinpointing the exact location of cracks, bellies, or tree roots without digging up your yard first.
4. How to Tell if the Issue is the Municipal Sewer System
Sometimes, you do everything right, and the problem still lies with the city’s infrastructure.Here are the clearest indicators that the municipal sewer system is failing:
- Your neighbors are flooding, too: If the houses to your left, right, and across the street are all experiencing gurgling toilets and shower backups at the exact same time, the city main is overwhelmed.
- Manhole overflows: If you look out your window and see water bubbling up out of the manhole covers in the street, the municipal system has reached maximum capacity.
- It only happens during torrential downpours: If your plumbing works flawlessly 364 days a year and only backs up during a 100-year storm event, it is highly likely the city main was simply overloaded by Inflow and Infiltration.
If you suspect the city line is failing, our Long Beach Plumbing experts recommend contacting your local public works department or city water authority immediately to report the street-level backup. Document the damage with photos and videos for potential insurance or city liability claims.
5. What to Do When the Rain Causes a Backup
If you are actively experiencing a drain backup during a rainstorm, taking immediate action can save you thousands of dollars in water damage and health hazards.
- Stop running water indoors: Turn off your washing machine, dishwasher, and do not flush the toilets. You do not want to add more water to an already blocked system.
- Locate your sewer cleanout: This is a capped pipe, usually located in your yard or near the foundation. Unscrewing this cap can relieve the pressure, allowing the sewage to spill into your yard rather than onto your living room carpet.
- Install a Backwater Valve: To prevent future storm-related flooding, our Long Beach Plumbing experts recommend installing a backwater valve (also known as a backflow preventer). This device is installed on your sewer lateral. It has a one-way flap that allows your wastewater to flow out to the city, but if the city sewer surges, the flap automatically locks shut, physically blocking city sewage from flowing backward into your home.
- Call a Professional: Sewage contains dangerous pathogens and bacteria. Professional plumbers have the hydro-jetting equipment, protective gear, and diagnostic tools to safely resolve the issue.
6. Why Choose A1 Best Plumbing?
Navigating sewer backups requires precision, expertise, and the right technology. At A1 Best Plumbing, we specialize in distinguishing between lateral line failures and municipal overloads. We provide transparent diagnostics, fair pricing, and long-lasting solutions like trenchless sewer repair and backwater valve installations.
Ultimately, our Long Beach Plumbing experts recommend that you never wait for a small gurgle to turn into a massive indoor flood. If you have noticed slow drains or have experienced a backup after a recent storm, act now.Contact A1 Best Plumbing today for a comprehensive sewer camera inspection, and secure your home’s plumbing against the next heavy rainfall!