Water Supply


The City of Toronto's source of water is Lake Ontario. But before the water reaches our taps, it undergoes a thorough cleansing process, and is then pumped, stored and distributed.

Who is responsible for water delivery?

Toronto Water is responsible for providing potable (drinkable) water to the local distribution systems of the City's community areas (former municipalities) – East York, Etobicoke, North York, Scarborough, Toronto, York, and to the southern portion of the Region of York. These areas are then responsible for delivering the water directly to residents and businesses. Not only does Toronto Water sell water to its residential, commercial and industrial customers, but also sells water to York Region.

In addition to being responsible for treating the water, Toronto Water is also charged with ensuring adequate water pressure and volume, and sustained quality throughout the system.

Since Toronto is built on the side of a long, sloping hill, the servicing of water to its communities is really an uphill battle. The first challenge is pumping.

What is pumping?

Centrifugal pumps are used to raise water pressure and to push the water from the lake level to the higher elevated areas.

To ensure adequate water pressure to the various local water distribution systems, the entire Toronto area is split into six levels or pressure zones, and each zone is further split into pressure districts. Each zone was selected based on the ground elevation range of its particular area of Toronto. Under normal pumping conditions, the pressure provided to the various zones varies from a minimum of 276 kPa to a maximum of 793 kPa.

The first stage of pumping water to the system occurs at the water treatment plant. After water is treated, it is pumped through a series of pipes to other pumping stations, reservoirs or points of supply for the local distribution systems. Because the water may have to be pumped one, two or three zones upward, Toronto has 18 pumping stations located in different pressure districts. Occasionally, there are high demands for water use in the various districts. In these instances, the standard water pressure that is required cannot be maintained by pumping stations alone. In this case, Toronto Water must draw water from its ground level reservoirs or elevated tanks.

What are ground level reservoirs and elevated tanks?

Ground level reservoirs and elevated tanks (both also known as floating reservoirs) are storage containers for water. They play an important role in the water distribution system because they provide stable water pressure in the district being served by the reservoir or tank and they maintain an adequate supply of water for distribution to districts during peak periods of water use which occurs in the summer lawn-watering season. These floating reservoirs also ensure a constant supply of water during emergencies such as fires, water main breaks, power outages and pumpage failures.

Toronto's 10 ground level reservoirs are enclosed concrete structures built into the ground. The roof is sloped and is covered with earth and grass. This allows the reservoir exterior to be landscaped for use as parkland and for recreational activities such as tennis and field sports.

The four elevated tanks are holding tanks located above ground at suitable elevations. They are smaller than ground level reservoirs and are located in smaller districts where there is less demand for large quantities of water or where there is a lack of space below ground. These holding tanks are made of steel and are connected to the distribution system.

Effective management of pumping and storage – using reservoir storage during peak times and replenishing storage with maximum pumping during off-peak times – provides the City with lower energy costs, while at the same time supporting the provincial management of power.

What is transmission?

The third component of delivery is transmission. This is the means of transporting large volumes of water from the treatment plants to pumping stations, reservoirs and tanks and to the local water distribution systems. Transmission involves a network of large pipes known as watermains for transporting water. Toronto Water's system contains approximately 520 kilometres of watermains that are between 150 mm and 2.5 metres in diameter. Most of the pipes in the system are made of steel, lined with cement mortar and encased in concrete. The older pipes are made of cast iron pipe. The water mains are generally buried in public streets about 1.5 metres deep. These mains have valves attached to them whose purpose is to stop or divert the flow, drain water or release air from the line. Access to these valves for cleaning and maintenance is gained through maintenance holes.

Large meters are installed in the mains at necessary locations to measure the flow of water from within the Toronto Water system for operational purposes, and to York Region for billing purposes.

How is the water distribution system monitored?

Toronto Water's four treatment plants, 18 pumping stations, 10 reservoirs and four elevated tanks are monitored by a computerized process control system located in the Transmission Control Centre. The computer system, overseen by a Pumping Control Officer, provides information on water pressures, flows, storage reservoir levels and chlorine residuals, as well as water and power consumption. In addition, equipment performance, flood conditions, temperatures in buildings and unauthorized entry are monitored. The Pumping Control Officer can control the operation of each pumping station and system valve operations to keep a proper balance between supply and demand while maintaining sufficient water pressure throughout. Pumping, storage and transmission operations are monitored 24 hours a day at the Transmission Control Centre.

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