Toronto has been affected by many widespread, and very costly, flooding events in the past several decades. The city was struck by flooding in 2000, 2005, and 2013. As climate change affects local weather patterns, it is expected that extreme rainfall events will only grow more common as time goes on. This makes the need for programs such as Toronto’s downspout disconnection program all the more important. When a downspout is connected directly to the local sewer system, either sanitary or storm, the water collected on the rooftop is deposited directly into the sewers. This can result in large volume of water entering the system and doing so very quickly. As a result, the sewer system, which is often combined in Toronto, can quickly be have its capacity overtopped and result in water and raw sewage backing up the private sewer lateral and into people’s homes. Furthermore, this problem is not limited to just those houses with a downspout connected to the system, it happens on a wide scale in which houses that are complying with the bylaw will be just as affected as those that are not. Another issue that arises with connected downspout is the fact that rainwater washing off of roofing can be quite polluted as particles of roofing material and other pollutant become entrained in the water as it flows over the roof. If a downspout instead feeds onto a lawn or garden, the plants and soil will act a filter for these pollutants and prevent them from being deposited into the nearby water bodies.
Responding to a series of costly flooding events, in 2007 the City of Toronto, Ontario decided to make its previously-voluntary downspout disconnections program mandatory in the hopes of reducing the volume of fresh water flowing into the sewer system during storm events. When a house’s downspout, the pipe that drains water from the rooftop, is connected directly a municipal sewer system the chance for sewer backup flooding increases. If a downspout is disconnected from the sewer system and instead drains onto a lawn or into a rain barrel, not only is less water in total entering the system, but it is also being deposited over a longer timeframe, giving the sewer system more time to discharge the water currently being handled and reducing the chances of that water backing up into homes.