How is the water treated so you can drink it?
1. Screen - A screen exists to stop large items that get caught in the pump and cannot complete the treatment process. For Example: branches
2. Low Lift Pump - this type of pump is used to lift water from the river into the Water Treatment Plant for the treatment process.
3. Mixer - the mixer allows for coagulation to occur, which is the addition of approved water treatment chemicals (Polyaluminum chloride - see Chemicals Used A.) to convert microscopic particles and other contaminants into larger and heavier particles
4. Clarifier - is a settling tank; clarifiers use sedimentation, a process that removes the majority of the larger particles from the mixer by settling them in tanks. Carbon (see Chemicals Used B.) is added at this point of the treatment process. Chlorine (see Chemicals Used C.) is added after the sedimentation process, before the water moves to the filtration treatment process.
5. Filtration - of the "settled" water, from the clarifier, removes most of the remaining particles to thousandths of a millimetre (too small to see).
6. UV Disinfectant 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 ultraviolet (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 (see Chemicals Used D.) are added after the UV Disinfectant stage, before the water is pumped to the storage reservoirs.
7. High Lift Pump - this type of pump discharges water into a nearby storage reservoir within Lethbridge
8. Storage Reservoir - this is the area where the treated water is stored and is pumped to houses, businesses and commercial operations within the area that the storage reservoir accommodates
9. Distribution Pumps - these pumps distribute the treated water from the storage reservoirs to the taps of the users of that reservoir.
Chemicals used at the City of Lethbridge Water Treatment:
A. Polyaluminum chloride (PAX-14 or ISO-PAC75) - 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 (Poly-DADMAC and ISOFLOC-HF410) – 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
B. Carbon - is used in the form of powdered activated carbon (PAC). 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 carbon added to the water
ranges from 1mg/L to 15mg/L. The concentration of carbon remaining in the
treated water is not detectable. The use of this chemical is not necessary to
produce potable quality water.
C. 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.
D. 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.
E. 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.