Water Treatment Process

Treatment of the water supply consists of:

1. Screening and oxidation of organics.
2. Ferric sulfate coagulation and hardness reduction.
3. Pre-chlorination and fluoridation.
4. Filtration by the use of rapid sand, and dual media filters.
5. Post chloramination and clear well storage prior to pumping to the distribution system.
6. Storage in reservoirs.

Step 1

Water is taken directly from the river through intakes upstream of the Water Treatment Plant at a rated capacity of 220,000 m³/day (48 Mgal/day).  It is screened and pumped from there to the Water Treatment Plant by pumps owned by the City and situated in the Queen Elizabeth Pumping Station. 

The intakes and low lift pumps at the Water Treatment Plant are used to increase the raw water pumping capacity during high demand periods (i.e. hot days in the summer) or when the main intake pumping station is shut down for service work.

New intakes located on the east river bank across from the Queen Elizabeth Pumping Station will be in service by fall 2011.   These intakes are designed with industry leading technology meeting all regulatory standards.

When the raw water reaches the Water Treatment Plant, potassium permanganate is added to address taste and odour problems with raw river water.

The water then enters the sand separator units to remove suspended sand particles before entering the clarifiers.

In the center mixing zone of the clarifier, ferric sulfate and lime are added.  Ferric sulfate is a coagulating agent used to agglomerate the solid particles into large groups of particles known as floc, thus increasing their size to a point where they settle more rapidly.

Lime reacts with suspended and dissolved solids in the water to reduce hardness and turbidity.  The hardness due to calcium and magnesium is reduced from approximately 180 to 120 mg/L as CaCO₃.

The concentration of floc in the clarifiers is carefully controlled and maintained as a dense circulating slurry.  The clear water is drawn off the top of the slurry, while excess floc is concentrated in a scavenging zone and removed.

Chlorine and fluoride are added after the hardness in the water has been reduced.  Chlorine disinfects the water  as the water travels through the settling basin allowing the chlorine to have adequate contact time to disinfect the water.   Fluoride helps to reduce tooth decay.

The sedimentation process is followed by filtration to reduce the turbidity of the water.  The filtration process involves passing water through beds of anthracite (coal) and sand.  The filtered water is collected in a clear well after it flows through the filter.

In the clear well, ammonium hydroxide is added to promote the formation of chloramines.  Chloramines have reduced disinfection capability than chlorine alone, but they remain active for a much longer period.  This extended period of activity allows disinfection to continue through the distribution system.

Chloramines are less volatile than chlorine gas and give off less taste and odour than would be the case with free chlorine in the water.

The filtered water is retained from 8 to 30 minutes in the clear well before it is pumped into the distribution system at a pressure of 690 kPa (100 psi).

There are three reservoirs within the City for storage as well as to provide additional pressure pumping capacity.  The 42^nd St. Reservoir has a capacity of 8 million gallons and a pumping capacity of 81,000 m³ /day.  The Acadia Reservoir has a capacity of 12 million gallons and a pumping capacity of 145,000 m³ /day.  The Avenue H Reservoir has a capacity of 4 million gallons.  It utilizes the pumps at the Water Treatment Plant. 

Highly trained plant operators in the control room closely monitor all aspects of the Water Treatment Plant, twenty-four hours a day, seven days a week. The on-site laboratory continuously tests the processes to ensure that the water going to the public meets or exceeds environmental standards.

The City's Water Treatment Plant exists to provide a dependable and adequate supply of safe, high quality, potable water to its customers. Under normal operating conditions, the supply meets the following criteria:

• All conditions specified in the provincial Permit to Operate.
• Water hardness does not exceed 140 mg/L (as CaCO₃.).
• Fluoride concentrations meet Saskatchewan Environment guidelines.
• Hourly demands are met with a minimum pressure of 38 psi at the main 93 percent of the time. Daily demands plus fire flow demands are met at a minimum pressure of 20 psi.
• Fire hydrants meet the minimum requirements of the Fire Underwriter's Survey 99 percent of the time.
• Water consumption is metered in accordance with American Water Works Association (AWWA) standards.

In the event of interruption in normal water supply, the following criteria are met:

• Following notification of a main break, normal service is restored within 24 hours in 95 percent of the occurrences and an alternate source is provided within 8 hours in 98 percent of the occurrences.
• During treatment plant failures, storage volumes can sustain a rationed supply for 48 hours.
• During a major city-wide power outage, standby equipment can sustain average annual consumption demands.

Water is supplied to SaskWater Corporation, within the terms of a Master Water Supply Agreement and in accordance with the City Policy C09-018 (Potable Waterline Connections), to serve water users outside the City's boundaries.