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Water Treatment Plant

Where does our water come from?

The City of Lethbridge gets all of its water from the Oldman River. A river is considered a surface water supply. Lethbridge do​es not use groundwater from wells. Our Water Treatment Plant processes river water into safe, healthy drinking water.

How is the drinking water tested to ensure its quality?

The certified operators at the treatment plant performed about 29,000 water tests as part of their daily routines  each year:
  • Daily water tests
  • Bacteria tests performed by the Provincial Public Health Laboratory each week
  • Monthly chemical analysis that includes metals and disinfection by-products
  • At least twice per year, treated water samples are subjected to a scan of 40 organic compounds, including pesticide chemicals, over 40 tests for metals, and other routine analysis
  • Over 32,000 tests are conducted on our treated water each year
View the Water Consumer Confidence Reports and Water Quality Reports for further information on how our drinking water is treated and tested.​​​

About the Water Treatment Plant in Lethbridge

The City of Lethbridge water distribution system consists of approximately 590 km of water main and 6 storage reservoirs with pump stations. The water mains and pump stations deliver water to residences and businesses throughout the city and neighbouring communities. 

The Water Treatment Plant draws our water supply from the Oldman River. The Plant is capable of treating 150 million litres of water per day and uses a multi-step treatment process.​​​​


How is the water treated so you can drink it?




Accordion Answer


The water enters the Water Treatment Plant from the Oldman River.


The water then enters the Water Treatment Plant, passing through screens, which filter the water of larger debris before entering the treatment process. A screen exists to stop large items that get caught in the pump and cannot complete the treatment process. For Example: branches.


This type of pump is used to lift water from the river into the Water Treatment Plant for the treatment process.


The mixer allows for coagulation to occur, which is the addition of approved water treatment chemicals (Polyaluminum chloride) to convert microscopic particles and other contaminants into larger and heavier particles .

Polyaluminum chloride  - is key to the particle removal processes of coagulation and flocculation. It transforms the naturally occurring microscopic particles found in the water into larger particles (a.k.a. floc) that can be settled or filtered from the water. Polyaluminum chloride is more effective in cold water and contains less aluminum than the historically used Aluminum Sulphate (alum). The dosage of polyaluminum chloride added to treat the water ranges from 20mg/L to 120mg/L. The concentration of polyaluminum chloride remaining in the treated water is not detectable. The use of this chemical is necessary to produce potable quality water. Polymers – organic polyelectrolytes – are occasionally used in small amounts to enhance flocculation under extreme conditions, particularly in cold water when the chemical reactions can occur more slowly. The dosage of polymers added to the water is 0.1mg/L to 1.0mg/L. The concentration of polymers remaining in the treated water is not detectable. The use of this chemical is necessary to produce potable quality water.


Clarifiers are settling tanks; clarifiers use sedimentation, a process that removes the majority of the larger particles from the mixer by settling them in tanks. Activated Carbon is added at this point of the treatment process.

Activated Carbon - is used in the form of powdered activated carbon (PAC). Activated Carbon absorbs organic compounds found in the water and is used as needed to control taste, odour, and colour in the water. The dosage of activated carbon added to the water ranges from 1mg/L to 15mg/L. The concentration of activated carbon remaining in the treated water is not detectable. The use of this chemical is not necessary to produce potable quality water.

Disinfection is the addition of chlorine, which disinfects the water so it is safe for drinking. Chlorine  is added after the sedimentation process, before the water moves to the filtration treatment process.

Chlorine - disinfects the water so that it is safe for drinking purposes. This chemical destroys micro-organisms such as bacteria and viruses in the water which can pose a threat to public health. The dosage of chlorine added to the water is 2mg/L to 4mg/L. The resulting concentration of chloramine in the treated water is 1.8mg/L to 2.2mg/L. The use of this chemical is necessary to produce potable quality water.

CLICK here to watch an additional sub-video which explains Coagulation, Clarification and Disinfection more in depth , or see "Other Videos" at the bottom of this page!

Filtration of the "settled" water, from the clarifier, removes most of the remaining particles to thousandths of a millimetre (too small to see).


Ultraviolet (UV) disinfection of the water with chlorine is a way to protect public health from disease causing organisms that can be found in the river. The risk to public health is reduced further by treatment with UV light. Before the water leaves the treatment plant, we combine the chlorine with ammonia to form chloramine. This reduces the formation of disinfection by-products, and ensures a long-lasting "residual" to protect our water against bacteria or other organisms on its journey to your home tap.


​The chemicals Ammonium and Fluoride are added after the UV Disinfectant stage, before the water is pumped to the storage reservoirs.

Ammonia - Ammonium Hydroxide - is used to combine with chlorine to form “Chloramine”. Chloramine maintains its disinfecting properties for a longer time than does free chlorine. This is particularly useful for long distribution mains and large storage reservoirs. The dosage of ammonia added to the water is 0.5mg/L to 1.0mg/L. The resulting concentration of chloramine in the treated water ranges from 1.8mg/L to 2.2mg/L. The use of this chemical is necessary to produce potable quality water.

Fluoride - Hydrofluorosilicic Acid - is added as a dental health measure to prevent tooth decay. Its application is authorized under City Bylaw # 3236 and has been added to the water in Lethbridge since 1974. The dosage of fluoride added to the water is 0.5mg/L to 0.7mg/L. The resulting concentration of fluoride in the treated water is 0.7mg/L to 0.9mg/L. The use of this chemical is not necessary to produce potable water.


This type of pump discharges water into a nearby storage reservoir within Lethbridge.


There are 6 storage reservoirs within Lethbridge, where treated water is stored.


These pumps distribute the treated water from the storage reservoirs to the taps of the users of that reservoir.


Water is pumped into the distribution system of the underground pipes, where it is sent to homes and businesses throughout the city and to surrounding communities.

Other Videos

Water Treatment Plant Coagulation, Clarification, and Disinfection




Water Treatment Plant Filtration and Ultraviolet (UV) Disinfection



Where is the Water Treatment Plant located?

The Plant site is on the east bank of the river, south of Whoop-Up Drive, and across the river from the University of Lethbridge. We process an average of about 53 million litres of high quality drinking water on a daily basis.

The maximum daily production in 2017 was 133.2 million litres, on July 18th.

For more information

Phone: 311 or 403-320-3111 (if outside of Lethbridge)
Online: Submit a service request