What is a Sewer Backup?


A sewer backup is the flooding of raw, untreated sewage into a home through drain pipes. This can happen because sanitary sewer lines are clogged because water levels in the soil around sewer lines are high (i.e., groundwater is entering sewer lines), or because manholes and other sewer system structures do not function properly.

What causes a sewer backup?

Sewer backups are caused by many different factors, which are outlined below.

  • Clogged lines – Blockage can be caused by grease, tree roots, baby wipes, rags or other debris that build up in the line over time. Some sources estimate that 40% of sewer backups are caused by grease buildup in lines leading to the sewer main. Grease accumulates in sewer lines from cooking fats and oils that are poured down the drain. These greases solidify over time, collecting dirt and other debris along the way until a backup occurs.
  • During periods of excessive rainfall – A sewer system that has the capacity to hold only a certain amount of stormwater during dry conditions will overflow when too much water is added, such as from heavy rainfall.
  • Inadequate pipe slope – In this situation, soil surrounding the sewer line is more porous on one side of the line than another, causing groundwater to pool against that side. The difference in soil porosity can result from natural or man-made causes (e.g., construction of roads, houses, or parking lots). If the water table is too close to the ground surface, groundwater seeps into sewer lines through cracked pipes and connections, faulty joints in PVC piping, poorly sealed cleanouts in clay pipe, and other defects.
  • Sanitary sewer flow obstructions – Tree roots and other debris may enter the pipe and cause a blockage, as can grease buildup in some cases. Other sources of blockages include damaged, sagging pipes; collapsed sections of piping under roads, sidewalks or driveways where heavy vehicles pass over them; broken pipes hidden in inaccessible areas, such as under slabs or in attics; improper grading that causes rainwater to pool around the pipe instead of draining away from it; deteriorated sewers due to age or neglect; and other sources.
  • Manhole obstructions – The top of a manhole may be obstructed by soil settlement or by cover plates installed upside down or askew.
  • Other infrastructure problems – Seepage from a sanitary sewer main into a storm drain system can back up the storm drain and cause flooding. Likewise, wastewater from a drain pipe may flow into a sanitary sewer line due to poor grading around the building, which causes water to pool next to the building foundation and enter the sanitary sewer line.
  • Pipe diameter and length – Longer pipes with the same diameter as shorter ones will have a greater capacity, so clogs are less likely to occur over time. Very short pipes may be susceptible to blockages due to insufficient slope or soil characteristics that tend to pool water next to the pipe.
  • Sewer system age and condition – Older sewer systems (i.e., those built before 1970) may be made of clay, which is more vulnerable to soil settlement that can crack the pipe or cause cover plates to shift over time. Some old pipes were designed with cleanouts at each joint; if these are not accessible for cleaning and inspection (or the section of sewer beyond the joint cannot be easily accessed), blockages may occur.

How much does it cost to repair a sewer backup?

Repairing a sewer backup can cost anywhere from $2,500 to $30,000 or more.

Are sewer backups covered by insurance?

Typically, sewer backups are not covered by homeowners’ insurance policies. Homeowner’s insurance will typically only cover damage due to sewer backup if the problem is caused by a pre-existing condition that was not disclosed to the insurer at the time of purchase (e.g., an underground leak that suddenly becomes severe enough to cause sewage backup).

Can sewer backup into the washing machine?

Yes. A sewer backup into your washing machine is one of the most common causes of sewage damage to a home.

Can sewer backup into the bathtub?

Sewage backups can enter through toilets and tubs with defective or loose connections; cracks in or damage to the toilet bowl, tub, or shower tile; and leaking hot water heaters.

How to prevent a sewer backup?

The simplest way to avoid problems is to regularly maintain your sewer line. A properly maintained line will likely have fewer obstructions, so it may clog more slowly when a blockage does occur. Regular maintenance can be especially effective in preventing grease buildup in the line.

Some cities have public works departments that clean out storm drains and sewers during regular maintenance. If your city does not do this, you should consider hiring a service to clean out the line at least once a year.

Is sewer backup dangerous?

Yes. Sewer backups can pose health risks if they cause raw sewage to flow into your home, including an increased risk of contracting diseases such as hepatitis A and E. coli 0157:H7 (a bacterium spread by contact with animal or human feces). Backed-up sewer water may also damage personal belongings in the home, including electronic equipment and furniture.

How do I report a sewer backup?

Call the Department of Public Works in your city to report a sewer backup. In some communities, this is also the department that will respond to the problem.

Is sewer backup coverage worth it?

In some cases, coverage for sewer backup may be worth the expense of an insurance policy. For example, if you live in a flood-prone region and your home is at risk of substantial damage from sewage backup (due to flooding or otherwise), sewer backup coverage may be more affordable than paying out-of-pocket for costly repairs.

Who is liable for sewer backup?

If the backup was caused by neglect on your part (such as failure to clean out clogs or maintain your line), you may be liable for the associated expenses. However, if negligence on the part of a city government contributed to the damage (for instance, if roads were not properly maintained and exposed your sewer lines to damage), they may be liable for the expenses.

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