In 1904, the sewer system consisted of 13 km of pipe that discharged directly into the river, then called the Belly River.
By 1906, most of the homes behind the business districts were connected to the sewer system and by 1908 the City was willing to provide water and sewer service anywhere “if the people were willing to put up the cost, to be reimbursed when the number of connections gives the revenue” (Lethbridge daily Herald, September 29, 1908).
In 1909, a further 3 km of sewer extensions was proposed, the majority of which had been requested through a petition.
The First Wastewater Treatment Plant
By 1910, the City’s sewage was causing serious contamination of the river, resulting in a number of typhoid epidemics downstream. The City’s first Wastewater Treatment Plant was designed and constructed, beginning operation at the end of 1912.
The Southside Plant was an innovation in its time being patented under the name of "Sewage Disposal Plant of Lethbridge, Canada." It boasted settling tanks, trickling filters and effluent chlorination treatment. In 1944 the plant was expanded to 6,600 cubic meters by the addition of two primary clarifiers, 2 sludge digesters, and a sludge drying bed. In 1959 the plant was increased again to accommodate 9,900 cubic meters.
The Second Wastewater Treatment Plant
In 1961, a second Wastewater Treatment Plant was constructed to accommodate wastewater from the growing industrial base in North Lethbridge. The North Plant was upgraded in 1966, 1972 and 1981. In 1987, in response to higher effluent quality standards imposed by Alberta Environment, the City began a $32,000,000 expansion of the North Plant. The expansion was completed in 1989, at which time the South Plant was decommissioned.
Biological Nutrient Removal (BNR)
Between 1994 and 1998, a new treatment process was piloted and implemented. The North 
Plant was a Conventional Activated Sludge System with a design capacity of 49 megalitres per day. The influent consisted of two separate wastewater trains: - The domestic stream consisted of residential and commercial customers.
- The Industrial stream consisted of two slaughterhouses, and five food processors.
The
upgrade of Lethbridge Wastewater Plant to the Lethbridge Environmental
Treatment Services began in April, of 1998.
The plant consisted of five parallel two-pass aeration tanks. These, in turn, were separated so one set of two, would handle the industry stream, and the other set of three, would handle the domestic stream.
The Conventional Activated Sludge System was designed to remove just BOD (Biological Oxygen Demand), The process enhanced the plant’s ability to remove nitrogen and phosphorus (biological nutrient removal or BNR). The upgrade also added ultraviolet disinfection of the treated effluent.
A second award followed this in 2002 given by the Oldman River Basin Water Quality Initiative. The City of Lethbridge Wastewater Treatment Plant was acknowledged for outstanding performance and lasting contribution to the protection of water quality in the Oldman River.
In 2001, the City of Lethbridge was recognized for its Biological Nutrient Reduction Process. The first was the Consulting Engineer of Alberta Showcase Award. This was as award of merit for the environment for the upgrading of the facility.
Cogeneration Units
In 2002, the plant was fitted with two cogeneration units. These units use digester gas to generate heat and electricity that are both used in the plant. . The purpose of the generators is to optimize the use of available digester gas for the production of heat and electrical power. In turn we reduce our emissions to the environment due to the lack of stack flaring. The upgrade included a building that housed 2, 16 cylinders Cat engines that have a rotative speed between 900- 1500 RPM and a generator output of 550 KW at continuous duty and 750 kW at standby duty. The motors have a minimum of 40% heat recovery during continuous duty, and cannot exceed 4.0 gm/kWh nitrogen oxide and 7.1 gm/kWh carbon monoxide. The upgrade also included the installation of two iron sponges to remove hydrogen sulfide from the digester gas to help our motors run more effectively and improve our air standards.
In 2007, the blowers and aeration system were upgraded to increase the efficiency of the BNR process and reduce energy consumption.
Regional Wastewater received from the Town of Coalhurst in 2012.
This marked the first new regional wastewater customer since the Agriculture Research Centre and Provincial Jail (1973), Fairview subdivision (1980), and the Rave Industrial Park (2000). Further, a wastewater forcemain from the Agropur cheese plant in Diamond City and the West Coast Reduction rendering facility north of the City was completed by the end of 2014.
2020 capital projects E-11 and E-12
These projects were made up of five components:
The first component was an influent channel modification. A new diversion channel from the existing influent channel was created. A twinning of the existing influent channel and a new connection to the existing South and Bridge Drive siphons was created.
The second component was a new Headworks. The construction consisted of four new bar screen 
channels with three new bar screens. Two screening washers/compactor/conveyors units were installed. Two grit removal units were added which consisted of two recessed impeller pumps, two grit washing units, two grit snail grit dewatering units and grit conveyance system that can feed either side of the headworks. Flow splitting channels to split screened and de-gritted primary influent between two new and two future primary clarifiers. A screenings and grit loading bay completed the headworks.
The third component was two 25 meter diameter circular primary clarifiers.
The fourth component was a primary effluent channel connecting the new primaries to the existing bioreactors .
The fifth component was the construction of the prim
ary sludge house for the new primaries. The building houses rotary lobe primary sludge and scum pumps. The sludge loop was connected to the pump house through a new utilidor to the existing galleries.
The hydraulic design basis used for all components was based on an 80 MLD average annual flow and a 160 MLD peak flow.
