The Sewer System

The City of Hamilton has three different types of sewers:

The sanitary sewer collects sewage and wastewater from toilets, bathtubs, sinks, floor drains and laundry machines in your home. Sanitary sewers are generally located under the roadways in front of your home. These sewers carry the wastewater to a wastewater plant for treatment. 

The storm sewer carries rainwater, melted snow and surface water from your home and roadways.  Catch basins that you see on the street capture water from the roadway and drain directly into the nearest creek, river or Hamilton Harbour. This water is not treated.

In the oldest areas of Hamilton, the City’s sewer system collects both sanitary sewage and stormwater into a single pipe called a combined sewer. The mixture, called combined sewage, is sent to the wastewater treatment plant for treatment.  During dry weather or small rainstorms, all combined sewage receives full treatment. During large rainstorms when flows exceed the capacity of the sewer system and the treatment plant, the excess flows, known as combined sewer overflows, are diverted into combined sewer overflow tanks.  

Combined Sewer Overflow tanks

Combined Sewer Overflow tanks, or CSO tanks, store excess combined sewage during rainstorms.  After the storm, the combined sewage within the CSO tanks goes through the distribution system to the wastewater treatment plant for treatment.  Solids, which settle to the bottom of the tank, are washed from the tank’s floor to reduce odours.  The wash water is collected in a trough at the bottom of the tank and pumped back into the combined sewer system for treatment.

During large rainstorms, diversions may be necessary when the combined sewer, the wastewater treatment plant and CSO tanks are full. Once full, some combined sewage goes to the waterways to minimize basement flooding and overloading the treatment plant.­­ 

The City currently has eight CSO tanks and one equalization tank in operation, providing a total storage volume of approximately 314,000 cubic metres. These storage tanks reduce the frequency of combined sewer overflows by 85% to 95% and the volume of the overflow by 90% to 95%.

Report a Sewer backup

If you have a sewer back up, call 905-546-2489. Staff can provide options for you and explain the Sewer Lateral Management program.