10 Causes of Sewer Backup and How to Fix Them

Here are the top 10 causes of sewer backups:

1. Tree Root Intrusion: Tree roots often seek out water and can penetrate sewer pipes through cracks or joints, causing blockages.
2. Grease, Oil, and Fat Buildup: Cooking oils and fats accumulate inside pipes, forming stubborn blockages and clogs over time.
3. Cracked or Collapsed Pipes: Old, corroded, or damaged pipes can break or collapse, leading to backups.
4. Non-flushable Items: Flushing items like wipes or paper towels can clog sewer lines and slow drainage.
5. Heavy Rainfall: Excessive rain can overwhelm sewer systems, causing flooding and backups.
6. Combined Sewer Overflows (CSO): In older cities, combined sewer systems can overflow during heavy storms, affecting residential areas.
7. Municipal Sewer Line Problems: Maintenance or blockage issues in the city’s sewer line can back up into your property, especially during repairs or construction.
8. Aged Infrastructure: Outdated plumbing systems are more prone to wear and tear, leading to blockages and failures.
9. Improper Sump Pump or Downspout Connections: Redirecting water into the sewer system with poorly connected sump pumps instead of storm drains can cause clogs and backups.
10. Flushing Hygiene Products: Many hygiene products and wipes do not break down and can create blockages in the sewer system.

Each of these causes can lead to significant plumbing issues, so it’s essential to understand the root of the problem to effectively address it.

1. Tree Root Intrusion into Sewer Lines

Roots naturally seek moisture and will infiltrate the sewer pipes if they have cracks or joints to access water. It is one of the most common causes of sewer backups. Once inside, roots can cause blockages by expanding and binding together, reducing the flow of wastewater. Some early signs of root intrusion include slow drainage, gurgling noises, frequent backups, and foul odors emanating from the drains. 

If this is left untreated, the root growth can cause a full blockage, causing significant damage to the pipes and even flooding your home, resulting in costly damage. In the following sections, we’ll cover effective ways to fix and prevent root intrusion, including chemical treatments, mechanical root removal, and trenchless pipe repair options. 

2. Fats, Oils, and Grease (FOG) Buildup in Pipes

Liquid fats, oils, and grease (FOG) are major substances behind sewer backups and are particularly common in kitchens. When grease enters your drains, it cools and solidifies on the pipe walls, slowly building up over time. Though they seem harmless, they create a hard, wax-like substance that blocks the flow of water, eventually leading to slow drains, blockages, or even full sewer backups. 

To fix grease buildup, homeowners can use enzyme cleaners to break down the grease or install grease traps to capture FOG before it enters the sewer line. In extreme cases, homeowners should schedule a professional hydro jetting service. Avoid disposing of oils and fats down the drain to minimize the risk of backups.

3. Cracked or Collapsed Sewer Pipes

As the sewer system ages, pipes made from outdated materials can weaken over time, leading to cracks or collapses. This is usually common in older homes with plumbing systems made from clay, cast iron, or steel pipes. Over time, these pipes become more brittle, and once the pipes crack, they become prone to root intrusion, debris buildup, and water infiltration. 

Some common causes of damage include ground settling, shifting soil, long-term corrosion, and nearby construction. In the worst cases, the pipes may collapse entirely, causing major backups and flooding. To resolve this issue, homeowners should schedule an inspection using a sewer camera to assess the damage and identify the issues early. Repair methods like pipe relining, trenchless repairs, or complete pipe replacement can fix the problem. 

4. Non-Flushable Items Blocking the System

Many products like baby wipes, paper towels, hygiene products, and cotton swabs don’t break down easily in the pipes as toilet paper does. These items can cause soft clogs that slowly obstruct the flow of waste, leading to eventual backups. Even items labeled as “flushable,” such as certain wipes, do not disintegrate quickly enough and can contribute to these blockages. 

To prevent this, these items should be disposed of in the trash and protect both household plumbing and the broader municipal sewer system from unnecessary damage and costly repairs. 

5. Heavy Rainfall Causing System Overflow

In areas with older or poor drainage systems, heavy rainfall can overwhelm municipal sewers, causing flooding and backups. When stormwater flows into the system, it can exceed the system’s capacity, leading to sewage backups in homes, streets, and basements. Overflow typically occurs when storm drains are clogged or when the main sewer line is overwhelmed.  

Some symptoms of overflow include water backing up through basement drains, sinks, or toilets, and in some cases, localized flooding. To prevent this, homeowners should install backwater valves to prevent reverse flow, maintain storm drains, and ensure sump pumps are functioning properly. These simple methods can help minimize damage during extreme weather.

6. Combined Sewer Overflow (CSO) Systems

In older cities, combined sewer systems (CSOs) carry both stormwater and household wastewater in a single pipe network. During heavy rainfall, the volume of water can exceed the system’s capacity, and untreated sewage may overflow into residential areas. This creates significant health and environmental risks, particularly when sewage backs up into homes or streets. 

Upgrading infrastructure to separate stormwater and wastewater systems is the long-term solution. For homeowners, installing backflow preventers and keeping drains clear can help reduce the impact of CSO issues. Many cities are now investing in sewer separation projects or green infrastructure to reduce CSO events and improve long-term water quality. 

7. Municipal Sewer Line Backups

Municipal sewer line backups occur when overflows or blockages in the city’s main sewer system cause wastewater to back up into individual homes. When municipal sewers become overloaded due to increased usage, construction, or even debris buildup, wastewater can back up into your home. Common causes of municipal backups include construction debris in the sewer lines, grease buildup, intrusive tree roots, or issues with sewer maintenance. When such issues arise, it’s crucial to report them to local authorities to ensure prompt investigation and response. Homeowners can install backflow preventers, or check valves, to prevent wastewater from entering their home in case of emergency. Regular maintenance and inspections of the local sewer system can help mitigate these risks. 

8. Aged or Deteriorating Pipe Infrastructure

Over time, pipes naturally deteriorate due to age, corrosion, and constant wear. Older plumbing systems made from materials like clay, cast iron, or steel are prone to cracking and breaking due to corrosion, soil pressure, and root intrusion. As these pipes weaken, they can cause slow drainage, leaks, or, in severe cases, backups. 

The key to preventing and solving this issue is regular pipe inspection with advanced techniques like camera inspections to detect early signs of wear. For long-term durability, repairing sections of pipes or replacing the entire system with materials like PVC or HDPE is recommended. These are more resistant to corrosion, wear, root intrusion, and shifting soil.  

9. Improper Sump Pump or Downspout Connections

When sump pumps or downspouts are improperly connected to the sewer system instead of directing rainwater to storm drains, the excess water can overload the sewage system. This creates serious problems and results in backups, particularly during heavy rainfall. Connecting stormwater to the sanitary sewer is illegal in most areas, as it overwhelms the system. 

Homeowners should have their plumbing system inspected to ensure that their sump pumps and downspouts are directed toward the yard or a proper stormwater drainage system. Additionally, checking for any illegal connections and redirecting them to the correct outlets, away from the foundation, is essential for preventing flooding and backups.

10. Flushing Wipes, Hygiene Products, or Paper Towels

Wipes, hygiene products, and paper towels are commonly labeled as flushable and are flushed down toilets, despite being non-degradable. Flushing wipes or towels is a leading cause of soft clogs in household plumbing. These items can easily clog pipes and create blockages in the sewer system, leading to backups in homes and municipal sewer systems. 

To prevent such problems, homeowners should flush only degradable papers. In addition, it can be fixed by a professional plumber who uses a combination of augering, water jetting, or camera inspections to clear the pipes. Homeowners and businesses should follow the “No flushing” policy for items like cotton swabs, baby wipes, and feminine hygiene products, and prevent future blockages.

How to Fix a Sewer Backup?

Fixing a sewer backup depends on accurately identifying the underlying cause. Whether it’s due to a blockage, system overload, or pipe damage, the solution will vary depending on the specific issue and severity. Once the issue is identified, several approaches can resolve the problem, from clearing blockages to repairing or replacing damaged pipes. 

Here’s how to address common sewer backup issues:

1. Mechanical rooting: If tree roots are causing the blockage, professional plumbers can use techniques like root cutting, chemical root killers, or hydro jetting to clear the lines.
2. Chemical Dissolvers: For grease blockages, enzyme cleaners or hydro jetting may be used to break down organic buildup and grease. It can be prevented by installing grease traps in kitchens.
3. Pipe Repairs or Replacement: Damaged pipes, whether cracked, collapsed, or corroded, may require repair through pipe relining or trenchless methods. In severe cases, the pipes may need to be replaced entirely.
4. Clearing Non-flushable Items: If non-flushable items have caused a clog, a professional will use specialized tools like augers or water jetting to remove the items and restore flow.
5. Preventing Municipal Sewer Overflows: For issues related to the municipal sewer system, solutions such as installing backflow preventers or maintaining proper drainage are necessary.

If you’re unsure how to proceed with a sewer backup, contacting a professional plumber is recommended to ensure the problem is resolved properly and safely.