Backwater valves are, effectively, a one-way gate that is placed inside the sanitary sewer lateral of a home. They allow for wastewater to flow out from the home into the sewer system, but prevent sewage from flowing into the home via the sewers during a flooding event. Research has consistently shown that these are an effective tool for the prevention residential flooding, which is a phenomenon that now consistently causes more than $2 billion in damages annually in Canada. However, a backflow valves does require maintenance in order to work properly. An analysis of Ottawa’s 2009 flood indicated that the most common point of failure was the valve cover, which was often not screwed into place adequately, causing eh system to fail. Other notable possible causes of backwater valve failure is a degradation of the O-rings in the system, preventing a complete seal, or the collection of debris under the gate itself, which can cause the gate the stick in the open position and thus rendering in unable to stop sewer backflow from entering a home. As the climate continues to change, it is likely that extreme rainfall events will become more common, necessitating a greater reliance on preventative devices like backwater flow valves.
In 2009, the City of Ottawa, Ontario, was subjected to a major rainstorm and flood and, in the aftermath, realized that the effective use of backwater valves was a critical, but secondary, line of defence against urban flooding. An analysis conducted after this flooding event found that out of some 1500 homes that received flood damage, about eight percent already had a backwater valve installed. The end result of a more detailed analysis of this problem indicated that backwater valves are indeed a useful tool in preventing flood damage but need support and maintenance in order to continue functioning properly. As they are located in homes, it is therefore paramount that the city educate homeowners on what backwater valves are, how they work, what protection they offer, and how to maintain that protection over time. This education was a key component of the 2009 by-law requiring the installation of backwater valves in all new homes.