Calgary's three wastewater treatment plants, measured: flows, process and published results

01 /Which plants treat Calgary's wastewater, and how much does each handle?

Three City plants take everything Calgary's sanitary system collects. The City's homeowner guide to the wastewater system names them, Bonnybrook, Fish Creek and Pine Creek, and the City's wastewater page says that together they meet the needs of more than one million Calgarians every day. The City's open data on treated effluent show how unevenly that work is shared.

Bonnybrook dominates in every year. In 2025 it carried about 79% of the three-plant total, Pine Creek about 16% and Fish Creek about 5%. A cubic metre is 1,000 litres, so an average 2025 day returned roughly 515 million litres of treated water to the river. The City's Fish Creek project page lists some of the south Calgary communities that plant serves: Deer Ridge, Deer Run, McKenzie Lake, Parkland and surrounding neighbourhoods.

02 /How do plant flows change through the year?

They rise when it rains, even though Calgary's sanitary and storm systems are separate. In January and February 2025, Bonnybrook averaged about 371,000 m³ a day. Its highest days that year all fell in late June and July, topping out at about 720,000 m³ on 22 July and about 717,000 m³ on 21 June. Pine Creek's busiest 2025 day, about 198,000 m³, was more than double its annual average.

People do not flush twice as much in July. The extra volume is water that reached the sanitary system through defects and improper connections: cracked service lines and joints, loose manhole lids in flooded streets, and yard drains or sump pumps tied into the sanitary side. Engineers call it inflow and infiltration. Part of it enters through private service lines, which is one reason a cracked lateral is a public problem as well as a private one. The mechanism is covered in sanitary vs storm sewers in Calgary.

The City has also published in-pipe measurements. Its Collection System Levels and Flows dataset holds seasonal readings, typically May to September, from flow meters in the sanitary system between 2005 and 2013. Both datasets are described in Calgary wastewater data and monitoring.

03 /What does each treatment stage remove, and how is it measured?

Treatment is a sequence of separations, and the City's effluent results track what each separation leaves behind. The stage descriptions below follow the City's homeowner guide; the right-hand column links each stage to the parameters in the City's published data.

Averaged over 2025, the City's data show total phosphorus of about 0.21 mg/L at Pine Creek and about 0.5 mg/L at Bonnybrook and Fish Creek, and carbonaceous biochemical oxygen demand of about 2.5 mg/L at Pine Creek, 3.4 at Bonnybrook and 8.0 at Fish Creek. Plants differ in design and approvals, so compare each with its own history rather than ranking them. The City's guide says its laboratories sample every stage, every day of the year, to meet provincial standards.

04 /What happens to the solids and the energy they contain?

Sludge from the clarifiers becomes a resource. According to the City's homeowner guide, it is thickened, partly fermented to feed the bioreactors, and then digested in warm, oxygen-free tanks for about 25 days. Digestion converts organic matter into water, methane and carbon dioxide, and the City uses the methane as fuel for heat and electricity at its plants.

The City says Calgro, which has run for more than 30 years, supplies nutrients for crops such as cereal grains, trees, sod, small oilseeds and dried legumes, and that the water pressed out during dewatering returns to the start of treatment.

05 /How are the plants being upgraded?

The biggest published change is at Fish Creek. The City's project page states that the plant can currently run at only about 30 per cent of its capacity, and that the upgrade will let it run safely at full capacity, improve treatment for regulatory compliance and add odour control. The page also estimates odour levels about five times lower at the plant boundary and three times lower at the nearest homes once work is complete.

Schedules for projects this size move, so check the City's page for the current plan. Odour from the plants, and the biofilters planned at Fish Creek, are discussed in sewer smells in Calgary. The flow table above is a useful companion: as Fish Creek's capacity returns, its share of the south's flow may change, and the effluent data will show it.

06 /Why does the treatment plant matter to a homeowner?

Because the plant only sees what survives the trip, and your service line is the first part of that trip. Under the ownership split the City publishes, the street-side length of each connection is municipal and the house-side length is yours. A private line that leaks lets groundwater in, adding to wet-weather flows at the plant, and a private line that clogs backs sewage into a basement before anything reaches treatment. Bonnybrook also receives flow from neighbouring municipalities, including Airdrie, whose new connection is described in the Airdrie–Calgary wastewater pipeline. What happened when a pipe carrying raw sewage to Bonnybrook failed under the river in 2025 is covered in sewage leaks and the Bow River.

• Toilets: the City's rule is pee, poo and toilet paper only; wipes, floss and hygiene products go in the garbage.
• Kitchens: fats, oils and grease go in the green cart.
• Medicines: return them to a pharmacy.
• Your line: know what the City recorded for your connection with the Service Line Lookup, and see the full path in how Calgary's sewer system works.

For practical help when something backs up, CalgarySewers.com is this network's Calgary help desk. If you want your own line inspected, request quotes.

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