More often than not, basement flooding is a result of overland flooding, infiltration flooding or sewer backup, or a combination of two or all three of these types of flooding.

Sanitary sewage is generated by the use of toilets, sinks, drains and other home water uses. Because this type of sewage contains a high degree of contaminants and can pose a significant risk to human health and the environment, it requires treatment at sewage treatment facilities before it is released back into the environment. Sanitary sewage is collected through sanitary sewer laterals, which connect homes and buildings to underground sanitary sewer pipes.

Storm sewage consists of excess surface water, resulting from rainfall or snowmelt that has collected in streets, sidewalks, roofs and parking lots in urban areas. Various methods are used to channel this water to underground storm sewer pipes, including swales and catch basins. Although storm sewage is significantly cleaner than sanitary sewage, it can be contaminated with pet waste, salt and other contaminants picked up from city streets and other urban surfaces.

In most cases, your neighbourhood is serviced by underground sewage pipes that are either combined, separated or partially separated. These pipes carry either sanitary sewage, storm sewage, or a combination of both to sanitary sewage treatment facilities and nearby lakes, streams and rivers.

Combined sewer systems convey a combination of sanitary sewage and storm sewage, which is conveyed to sewage treatment facilities before being released into local surface water, including lakes, streams and rivers.

Combined sewers are designed to automatically bypass treatment facilities and re-route excess sewage to local surface water bodies when they become overwhelmed. This automatic bypass is called a combined sewer overflow (CSO), and it helps to protect sewage treatment facilities from damage and also helps to reduce the chances of sewer backup in buildings. However, as CSOs result in the release of raw, untreated sewage, they can have a significant negative impact on local surface water quality. Reduced water quality can have a negative impact on aquatic life, and can also reduce the recreational qualities of lakes and rivers. As homeowners’ weeping tile and downspout connections can contribute a substantial amount of water to the combined sewer, they can increase the chances that CSOs will occur.

Separated sewer systems have two individual pipes that are designed to convey only sanitary sewage and only storm sewage. The separation of the different types of sewage allows municipal engineers to direct sanitary sewage to treatment facilities, while storm sewage is allowed to flow into nearby lakes, streams and rivers with less intensive treatment. In some cases, neighbourhoods are serviced by partially separated sewers, which include sections that are combined and sections that are separated.

Sewer backup can happen when municipal sanitary, combined, or storm sewer systems receive more water than they can handle. Excess water can cause the sewers to "surcharge," and push water backwards through home sewer laterals and cause sewage to backup into the home through basement floor drains, toilets and sinks. Excessive surcharge in the municipal sewer can create high pressures around basement floors and the foundation, which can cause structural damage to the home. For example, excess pressure in pipes beneath the home can result in heaving of basement floors, especially when improper backwater valves are used. When weeping tiles are connected to the municipal system through sanitary sewer laterals or storm sewer laterals, sewage can be forced back into the weeping tiles, resulting in possible structural damage to the home.

If a home has a storm sewer lateral and the municipal storm sewer surcharges, water can be forced out of the storm sewer lateral and can enter the sanitary sewer lateral, resulting in sewer backup in the home and can also contribute to sewer backup in the neighbourhood.

Make sure you know your coverage: Sewer backup

> Most insurance companies will provide coverage for sewer backup damages. Sewer backup coverage is often included in home insurance policies, but in many cases a separate endorsement must be purchased for this type of coverage.

>  Not everyone’s insurance policy is the same: Talk to your insurance provider or broker to find out if you have coverage for sewer backup damage.

Have you made an insurance claim for sewer backup damages in the past?

There have been cases where homeowners who’ve made a claim for sewer backup damage have had difficulty in receiving payouts for later sewer backup damages.

> In some cases, homeowners who have made repeated claims for sewer backup damage have experienced capping of their eligible sewer backup payouts, or cancellation of sewer backup coverage altogether.

> If you have made a claim for sewer backup damage, talk to your insurance provider or broker to find out if it affected your sewer backup coverage.