Private realm rainwater management

In a combined sewer system, rainwater runoff is combined in a single pipe with wastewater from homes, businesses, and industry. During drier weather, the rainwater and wastewater are both carried to the sewage treatment plant. In heavy rains, however, high volumes of rainwater can exceed the capacity of a combined sewer system. The excess, untreated mix of rainwater and sanitary sewage overflows and empties directly into our waterways, which may also be habitat for aquatic species.

Contaminants are introduced into rainwater from a variety of sources, including air deposition, wearing of building and infrastructure materials, motor vehicles, litter, and fertilizers. Untreated rainwater runoff carries these to nearby waterbodies, reducing water quality, impacting aquatic life and public uses. 

By 2050, Vancouver is expecting a 5% increase in the volume of winter rain with slightly larger increases in spring and fall. It is also anticipated that Vancouver will see a 19% decrease in rain during the summer. Further, extreme rainfall events are projected to increase in frequency and intensify overall with 63% more rain on extremely wet days. These factors could lead to increased surface flooding, sewer back-ups, and combined sewer overflows.

A pervious surface allows water to penetrate through to the ground underneath rather than becoming runoff. As Vancouver developed over its history, the city has experienced a general loss of pervious surfaces and an increase in impervious surfaces that prevent water infiltration. Several consequential side effects result from this, including greater likelihood of surface flooding, increased contamination of local waterbodies, and reduced recharge to groundwater resources.

Flooding may occur due to unintended rainwater entering buildings, exceeded sewer system capacity, developments being built on a floodplain, construction dewatering, or other causes related to rainwater. Also, climate change is expected to cause higher intensity rainfall exacerbated by rising sea levels, increased intensity and duration of storms, or both. As such, flooding is of particular concern during wet seasons.

Vancouver’s population is expected to grow over the coming decades. Each new resident will use water that goes into sewers for treatment. Properties are also densifying to accommodate this influx of residents, which has resulted in more impermeable surfaces that channel storm water directly into sewers. These factors combine to place additional strain on the existing sewer capacity.

The core of the existing sewer system in Vancouver was designed in the early-mid 20th century. The deployment of water-efficient fixtures and appliances, and green rainwater infrastructure, extends the limited capacity of the existing sewer and drainage infrastructure.

• Building By-law External website, opens in new tab
• Sewer and Watercourse By-law PDF file (343 KB)
• Zoning and Development By-law
• Cambie Corridor Utilities Servicing Plan PDF file (5 MB)
• Green Buildings Policy for Rezonings PDF file (188 KB)
• Rezoning Policy for Sustainable Large Developments PDF file (378 KB)
• Citywide Integrated Rainwater Management Plan
• Rain City Strategy PDF file (21 MB)
• Urban Forest Strategy PDF file (14 MB)
• Bulletin 2019-008-PL - Siting requirements for on-site infiltration systems PDF file (198 KB)
• Bulletin 2008-007-EV/PL – Parkade drainage treatment system PDF file (229 KB)
• Bulletin 2000-058-PL – Separation of roof drainage and foundation drains PDF file (232 KB)
• Bulletin 2000-001-BU/PL – Lot drainage requirements for new homes PDF file (94 KB)