The water storage system
Storage in a water works system may take one of several forms. Some systems, due to local needs, store their source water in large natural or man made reservoirs, essentially small lakes. These are often created by the damming of mountain streams, and in many cases, normal recreational activities are permitted.
In Toronto, with abundant supply available from Lake Ontario, such reservoirs are unnecessary and water storage facilities consist of "in-system storage" provided by treatment plant, ground level reservoirs and elevated tanks.
In-system storage is provided for the following reasons:
- Water treatment plant reservoirs provide flexibility in plant operation, allowing the quantity of water produced to be either more or less than the quantity pumped, with the reservoir taking up the slack. This allows continuation of production during low consumption periods and continuation of pumping during short term plant outages. In-plant storage in the City's system consists of 208.5 megalitres (ML) as follows: Scarborough Pumping Station – 25; R. C. Harris Treatment Plant – 54; Island Treatment Plant – 34; R. L. Clark Treatment Plant – 27; Frank J. Horgan Treatment Plant – 68.
- Ground level reservoirs and elevated tanks provide capacity to permit a constant rate of pumpage, with demand in excess of pumpage being provided from the reservoir. Pumpage surplus to demand would be transmitted to the reservoir. This allows more economical selection and operation of pumping equipment.
- Storage in elevated reservoirs also provides requirements for fire emergencies. The availability of specified fire flows, as established by the Insurance Underwriters, can greatly reduce fire insurance premium costs. The presence of the elevated storage in reservoirs is a major factor in ensuring that the required fire flows are available.
- Storage in elevated reservoirs provide capacity for emergencies other than fire, including water main breaks and power or pumpage failures.
- A primary function of the elevated storage is the maintenance of a reasonably constant pressure on the district served by the reservoir. All pumps in a district provide pressure sufficient to pump water to the top water level of a reservoir. The minimum pressure in a district will occur should all pumps stop with pressure provided by the static head of the reservoir.
- Ground level reservoirs provide flexible suction storage for an adjacent pumping station pumping to a higher district, with such needs being separate from the emergency requirement on the district on which the reservoir serves.
- Storage capacity allows for the cost-effective management of energy use by:
- minimizing pumpage during the day while maximizing he use of reservoir storage
- maximizing pumpage during off-hours to replenish reservoirs
At the present time, the system includes ten major ground level reservoirs which are totally enclosed. The system also includes four elevated tanks, which, being of small capacity, are only suitable for small areas.
All of our reservoirs are landscaped and maintained as open space for the enjoyment of Toronto citizens. In addition, the surface area of some of them is leased to local Parks Departments for recreational purposes.