Climate change is expected to significantly increase the frequency and severity of extreme rainfall across Canada. Sewer backup flooding occurs when a sewer system is inundated with more water than it has the capacity to handle. When this happens, it is possible for the excess water to be forced back up the sewer lateral and into homes. This problem is exacerbated by the high degree of impermeable surfaces in urban areas, as well as high levels of inflow and infiltration into the sewer systems by broken sewer pipes and poorly-sealed connections. Both combined and separated systems are vulnerable to this type of event. Sewer backflow valves are a cheap and easily installed during the construction phase of home development. These devices all for household wastewater to flow out into the sewer network, but prevent backflow from said network from entering the home in the event of flooding. At the time of writing, the provincial building code required backup valves in new homes only “where a building drain or a branch may be subject to backflow”. The unclear and non-specific wording of the legislation is problematic. Some jurisdictions would apply these conditions only if an existing history of flooding is present, but recent research has indicated that all homes connected to public underground sanitary sewer systems have the potential to experience sewer back up.
Taking a proactive approach to the risks posed by sewer backup flooding, in 2013 the Town of Collingwood, Ontario, legislated that all new homes must be constructed with a backwater valve. In the event of a heavy rainfall, it is often the case that the municipal sewer system will be unable to handle the rapid influx of water. In this situation, the excess water will have no place to go but up through the sanitary sewer laterals, backing up raw sewage into homes. This is not a small issue, with an estimated $2 billion in damages caused by sewer backup flooding every year in Canada. A backflow valve is essentially a simple one-way gate that allows household sewage to flow out into the sanitary sewer but prevents sewage from travelling back into the home. These devices are relatively cheap, costing around $250 on average and can be installed for very little additional costs during the home construction phase.