Treatment Process

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Treatment Process

Drinking water undergoes a number of tests and treatment processes before it arrives at its destination: your household or business site. These include:

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Filtration

Seymour-Capilano Drinking Water Filtration Project (2003 – 2009)
In 2002, the Greater Vancouver Water District (GVWD) Board approved construction of the Seymour-Capilano Filtration Plant (SCFP) near Rice Lake in the Lower Seymour Conservation Reserve (LSCR). The filtration plant will cover about eight hectares and filter up to 1.8 billion litres of water a day. Also, the plant will convey water from the Capilano watershed through twin tunnels joining the Capilano and watersheds. Plant facilities are now being built at the Seymour and Capilano sources.

More on the Seymour Capilano Projects

Primary disinfection

Primary disinfection kills bacteria and viruses and makes water safe for drinking.

Coquitlam Ozone Primary Disinfection (1996 – 2000)
In 1996, the GVWD Board approved ozone as a primary disinfectant at the Coquitlam source. Ozone helps minimize chemical residuals in the water treatment process. Compared to chlorine, ozone:

requires a much shorter contact time with drinking water, reducing the need for pipelines, tunnels and land acquisition;

provides better disinfection for water-borne microorganisms and pathogens, including Giardia; and

significantly reduces the by-products of chlorine disinfection.

Coquitlam Ultraviolet Disinfection (2006 – 2010)
In 2005, in response to changes to the Canadian Drinking Water Quality Guidelines, the GVWD Board approved an upgrade of the Coquitlam facility to include ultraviolet (UV) primary disinfection. A combination of ozone and UV treatment is an effective way to eliminate Giardia and Cryptosporidium. This project may also replace the need for more filtration at Coquitlam, which has significantly less potential for turbidity than sources at Seymour or Capilano.

Existing Primary Disinfection
Existing facilities at Seymour and Capilano presently use chlorine for primary disinfection. However, these facilities will be phased out when the SCFP is brought on line in 2008 and the twin tunnels project is completed in 2009.

Secondary disinfection

As water flows through the distribution system, the disinfectant used during the primary treatment stage gradually breaks down, creating the potential for harmful bacteria growth. Secondary disinfection uses chlorine to prevent this from happening as water travels to homes, businesses, and industries. Ozone cannot be used as a secondary disinfectant because it breaks down too quickly. UV treatment also is not an option, since it leaves no residual disinfectant in the water.

Distribution system water quality

Since 1995, a number of system enhancements have increased water quality:

1995 - Vancouver began cycling the water kept in its 20 storage reservoirs to maintain water quality

1996 - Member municipalities began annual flushing and cleaning programs. Flushing cleans main pipes and helps reduce the requirement for secondary disinfection stations. This minimizes the volume of chemical residuals in the water.

1998 to Present - The GVWD boosted secondary disinfection by adding eight rechlorination stations

1999 - The Westerly Transfer was completed, allowing large volumes of water to be moved from the Coquitlam Reservoir to the west of the region during periods of high turbidity at the Capilano or Seymour source.

Corrosion control

The low mineral content in Metro Vancouver’s raw water sources means tap water is very soft. While this is good for bathing and laundry, it is corrosive to plumbing. For this reason, since 1998 at Seymour and 2000 at Coquitlam, Metro Vancouver has been adding low levels of soda ash (sodium carbonate) to water to reduce its corrosiveness. Field studies demonstrated this has been very effective at reducing copper corrosion. Currently there is no corrosion control for Capilano water, but the Seymour Capilano Filtration Plant, once it starts treating Capilano water, will use lime (calcium hydroxide) and carbon dioxide for corrosion control.