Sewer Backup Vs. Flooding: What are the differences?

Sewer backups and flooding are two different but connected. Sewer backups usually occur when water overflows from a sink, bathtub, toilet, or drain system. At the same time, a flood situation arises when there is continuous heavy rain or snowfall for a few days.

Canada’s urban and rural areas face problems due to aging infrastructure, climate change, and urbanization, which contribute to increased sewer backups and flooding issues.

Canadian residents need to understand the difference between basement drain backup and flooding to take effective preventive precautions against all new situations. In this article, we will explain the difference between sewer backups and flooding so you can be prepared for any sewer backup and flood-related issues. If your house is already facing such a situation you need to take immediate action by calling a professional restoration team to protect your house from further damages.

What is a sewer backup?

The overflow of dirty/wastewater from the kitchen sink, bathtub, drain, etc. is called sewer backup. This occurs when the flow of wastewater backs up from the plumbing system into a property, especially due to a blockage or overload in a public sewer system or private sewer system. This may result in property damage and health risks.

❖    Causes of sewer backup

1.    Blockages:
  • The collection of solid wastage, grease, sanitary pads, and other elements in the basement drain pipes creates a blockage.
  • Tree roots can penetrate the pipes of the sewer while searching for water. This situation leads to blockages and damage to the pipes.
2.    Heavy Rainfall and Stormwater Infiltration:
  • Due to heavy rainfall, the drainage system gets blocked. When the system exceeds capacity it results in sewage backups.
3.    Defective Or Fruitless Sewage System:
  • Aging infrastructure can contribute to sewer backups by cracking, broking, and collapsing pipes.
  • Sewage systems can occur in backup situations when they are not inspected, upkeep, or repaired on time.
4.    Inappropriate Disposal Practices:
  • The disposal of items like grease, sanitary napkins, and other biodegradables can cause clogging drains.
5.    Defects in the sewage system design:
  • Diminutive-sized or improperly designed sewage systems can limit their ability to hold the volume of wastewater. Causing sewage backup during heavy use or heavy rainfall.
  • Heavy rain can cause overflows or backups in areas with combined sewer systems that manage both stormwater and sewage. Because the system has been built to release excess water to prevent floods.
6.    Unlawful connections and cross-contamination:
  • Improper connections such as sump pumps or storm drains when connected to sanitary sewer systems can cause sewer backups.

What is flooding?

Generally, an overflow of water on dry land is called a flood. This occurs due to heavy rainfall, storms, or melting snow. This may submerge low-lying areas causing damage to property and infrastructure.

❖   Causes of Flooding:

flooding can occur due to both natural and man-made factors. Here are some frequent causes that are leading to flooding:

1.    Extreme rainfall:

Extreme and prolonged rains lead to excessive accumulation of water leading to the possibility of flooding.

2.   Whirlwinds :

Tornadoes may result in flooding of coastal areas, which may lead to sea level rise due to the powerful winds associated with the storm.

3.    Ice Melting :

During warm weather or a sudden temperature rise, snow melts faster which can increase runoff and potential flooding.

4.    Ice jams:

Ice breaks on rivers can lead to ice jams in colder regions, impending water flow, and creating a risk of localized flooding.

5.    Rapid inundation:

Sometimes the rapid onset of heavy rainfall within a short period causes sudden flooding of local drainage systems.

6.    River Flooding:

The overflow of rivers and streams caused by extreme rainfall, melting ice, or a combination of both can result in river flooding.

7.    Impassable surface and urban expansion:

Increased urban expansion with extensive paved or impassable surfaces reduces the natural absorption of rainwater leading to increased runoff and risk of flooding.

8.    Poor sewage infrastructure:

unmaintained or inadequate sewer systems can lead to flooding by stopping efficient water runoff.

9. Saturation of ground:

Prolonged rains or previous heavy rains can cause the saturated soil to not absorb excess water, resulting in increased chances of flooding.

10. Atmospheric changes:

Greater intensity and frequent storms as well as changing atmospheric patterns may increase the risk of flooding in certain regions.

Difference Between Sewer Backup & Flooding:

Assuredly! Sewer backups and flooding are quite different incidents, still they may share their similarities. Let’s discuss some key differences between them:

❖  Source of water:

  • Sewer backup includes surplus or dirty water from the sanitary drainage system. This condition occurs when the drainage system becomes blocked, damaged, or clogged due to some reason.
  • Excessive rainfall, storms, or overflow of rivers or other water bodies cause floods.

❖  Contents of water:

  • Sewer backups contain polluted water from sinks, toilets, and other household sewages. Which produce bacteria and other pathogens that pose a health risk.
  • Primarily, flooding may include clean water that may come from rain, rivers, or lakes, but it can become tainted when it comes in contact with pollutants, chemicals, or sewage.

❖  Causes:

  • Sewer backup problems occur when tree roots intrude in the pipes or system faults block sewer lines or overflow during heavy rains.
  • Flooding is caused by natural calamities like excessive rainfall, thunderstorms, faster melting of ice, or dam failure.

❖   Affected Areas: 

  • Drain backups cause damage to inner spaces, basements, and the ground floor.
  • Flooding can damage both inner and outer areas. which widely affects households, infrastructure, and landscapes.

❖   Hazard of health:

  • Sewage backup raises the risk of spreading diseases due to harmful microscopic organisms.
  • Although primarily clean, flooding water can be hazardous to health as it can carry contaminants (pollutants, chemicals, etc.) from different sources.

❖  Avoidance and reduction of harm:

  • Drain backup can be prevented by regularly maintaining drainage lines, avoiding inappropriate flushing, and installing backwater prevention devices.
  • Flooding prevention entails urban planning, flood barrier construction, and early warning systems. Mitigation involves elevating structures and managing water flow for effective disaster response.


Both flood damage and sewer backup damage are different, the causes are different and their effects are also different. Nevertheless, the only similarity in both situations is that both situations need to be resolved with immediate action. Both situations make you worried and confused as to what steps to take to get rid of this disaster. At ONT Restoration, we are here to help you in both types of situations, no matter how bad the situation is. We have years of experience and skilled technicians. We will be there to help you with just one phone call.

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