Sanitary sewers
Sanitary sewers transport wastewater released from a drain, toilet, sink or appliance such as a clothes or dishwasher. This wastewater from residences and businesses flows to treatment plants where it is cleaned before being released into Lake Ontario.

Storm sewers
Storm sewers capture rainwater or snowmelt from residential and commercial properties. This water flows into nearby watercourses or the lake. Watercourses include creeks, streams and rivers – natural, concrete channels or underground pipes – that carry water, including stormwater and snowmelt from catchbasins into Lake Ontario.

Combined sewers
In one of the city's older areas, the sewer serving your property may be a combined sewer. In a combined sewer, there is only one pipe which carries both sanitary and storm drainage. During dry weather, combined sewers carry all contents to treatment plants. However, during wet weather, the volume of water may exceed the treatment plant's capacity and some of the water overflows untreated into the lake. The storm sewers will carry stormwater and snowmelt and the old combined sewer will handle sanitary sewage only, eliminating the overflow in wet weather.

The process
Sewers operate by gravity, flowing downhill from the small-diameter pipes of your connection and the sewers on your street to the huge trunk sewer mains that take flows to their final destinations. The City maintains 510 kilometres of huge trunk mains, 9,977 kilometres of local sewers and 463,300 sewer connections. Sewers built where land slopes uphill require pumping stations to lift flows high enough again to function by gravity. The city operates 45 pumping stations and five storage and detention tanks.

Sanitary sewage flows to a treatment plant where contaminants are removed before the water is released into Lake Ontario.

Storm sewers flow into watercourses which include local creeks, streams, rivers and the concrete channels that carry water through the city to Lake Ontario.

How long will it take?
The average speed of flow in a sanitary sewer is two metres per second. That means that wastewater entering the system 16 kilometres from the treatment plant will reach it in approximately two and a half hours. A sewer flows at maximum velocity when the pipe is 83 per cent full. The deeper the flow - the faster it moves - up to that magic number of 83 per cent. Above that percentage, it again slows. The average temperature in the sanitary sewer system is 13oC in both summer and winter.

Once the flow reaches the treatment plant, it takes approximately 10 ½ hours to process the wastewater and release it as clean water into the lake. As in the sewer system, the higher the flow - the faster it is processed.

Stormwater retention areas are designed to capture the first 25 millimetres of rainwater in every storm and to then discharge it slowly back into the storm sewer system over a 24-hour period. This is the part of a storm that washes most of the pollutants such as oil from parking lots, driveways, roads and other surfaces into the storm sewer system. While the water is held in the retention area, a large portion of the pollutants settles. This function not only reduces the likelihood of flooding by reducing the volume of water in the storm sewers during heavy rain but also reduces the number and volume of pollutants flowing into the watercourses.

Did you know?
We have a scheduled maintenance program where all sewers are examined and necessary repairs are carried out. All watercourses also have an annual maintenance program and reconstruction and naturalization are carried out as necessary.

If you experience trouble with your sewer connection, you should call your community office at 311 since each area has its own policy. Your community office may also provide information on the location of your drain plan (from street line into your house), your city-owned connection (from the street line to the pipes in the roadway) as well as how to obtain a new sewer connection if necessary.

A little caution can really pay off – or how to prevent expensive sewer repairs and preserve the environment.
You can assist in the trouble-free function of sanitary sewers by ensuring that foreign objects such as diapers or children's toys do not enter the system. Disposing of quantities of cooking fats into your drains can result in serious and expensive blockages.

You can also help to reduce the pollution of our watercourses and Lake Ontario by not draining swimming pools onto the roadway or allowing soapy water from car washing to run onto the road and down catchbasins. Please don't dump anything into catchbasins. They are meant to receive only rainwater and snowmelt. If you notice someone dumping into catchbasins or any unusual substance in a watercourse, please report it by calling 311 so we can clean it up and minimize damage.