Watermains and watermain breaks
- Water is delivered from the city’s water treatment plants to pumping stations, reservoirs and tanks, and on to customers through large pipes known as watermains.
- The City of Toronto’s water distribution system consists of 5,850 km of watermains.
- Most watermains are metallic (made of cast iron or ductile iron).
- The average age of Toronto’s watermains is 55 years, with about 17 per cent over 80 years of age and 6.5 per cent over 100 years old.
- Surprisingly, many pipes are older than their theoretical service life of about 80 years.
- Watermain pipes are buried in public streets, about 1.5 m deep, just below the area where frost ends or “the frost line.”
- On average, Toronto experiences 1,300 watermain breaks each year.
- Small-diameter watermains of 150 mm or less represent only 55 per cent of the City’s total infrastructure, yet account for a large proportion of watermain breaks.
- Generally, small watermains are more likely to break because they have thinner pipe walls, making them more vulnerable to the effects of corrosion.
- A recent study of watermain breaks in Toronto indicated that small cast iron watermains constructed in the 1950s and 1960s are the most prone to failure, accounting for almost 93 per cent of breaks. These pipes are a focus of the City’s watermain replacement program.
- Toronto Water has embarked upon a comprehensive infrastructure renewal program. In 2007, Toronto City Council approved an $87.7 million program directed at renewing its aging watermain infrastructure.
Main causes of watermain breaks
Corrosion is a process by which metals break down due to chemical or electrochemical reactions with the environment. Corrosion can cause ‘pits’ to develop into small holes in cast iron or ductile iron pipes. The highest corrosion rates occur on watermains with copper service connections located in soils such as clay. These types of soils can be found in the Etobicoke, North York and Scarborough areas. The added moisture caused by a watermain leak can reduce the soil resistance and result in increased rates of external corrosion. Leaks can also erode the ground or ‘bedding’ surrounding a watermain, ultimately causing the piping to collapse. Additionally, cast iron watermains with sulphur-mortar joints are more susceptible to corrosion and pitting around the joints.
Another common cause of watermain breaks is related to the thickness of the pipe wall. Changes in manufacturing processes and materials led to the thinning of pipe walls between the 1800s and 1960s. As a result, watermains constructed during the late 19th century have thicker walls than watermains constructed during the 1950s and ‘60s. Small watermains with thinner pipe walls are more likely to break making them more vulnerable to the effects of corrosion. As a result, newer, thinner watermains, such as a 50-year-old watermain, may deliver a shorter service life than an older, thicker-walled watermain.
Watermain breaks can also be affected by temperature. Low temperatures can cause soil to freeze and expand, creating frost loading or force applied on the watermain. For this reason, the number of breaks is greater in the winter months. Prolonged periods of cold weather will result in an increase in the number of watermain breaks.
Other causes of watermain breaks
Size, type of joint, installation process and workmanship, manufacturer process, pipe depth, water pressure (such as high water pressures inside a pipe), leakage, ground water, seismic activity (waves of movement through the earth), disturbances and stray current interference (caused by rail transit systems).
Working to reduce watermain breaks
The City of Toronto carries out a variety of programs to help reduce watermain breaks, including:
The City replaces approximately 30 km of watermains each year. Priorities for watermain replacement are determined using a combination of the following factors; age, break frequency, material, pipe vintage, operational requests, hydraulic performance, future growth and to minimize cost and disruption to the local community in co-ordination with other construction programs (eg. road, sewer, gas, hydro, etc).
One of the most important preventative maintenance programs is the cathodic protection of watermains. To help reduce the corrosion and extend the service life of a watermain, clone is installed that will corrode in place of the actual pipe. Cathodic protection is applied to cast iron and ductile iron pipes. Approximately 800 km of cast iron and ductile iron watermains (or 13.5% of the total system) have been cathodically protected. In 2008, the City of Toronto is planning to cathodically protect 130 km of watermains.
Cleaning and Cement Mortar Lining:
Another preventative maintenance program is the cleaning and cement mortar lining of watermains. This trenchless technology is designed to address rusty water concerns and improve hydraulic capacity. Rust build-up is removed on the inside of older watermains and the internal surface is lined with a thin layer of cement. Approximately 2,000 km of cast iron and ductile iron mains (or about 34 per cent of the total system) have been cleaned and cement mortar lined. The City spends an average $20 million annually on this program.
Structural Lining (Cured-in-place Pipe Insertion):
Another trenchless technology involves inserting a structural lining within the existing watermain network. Structural lining uses resin-impregnated fiberglass to form a new pipe wall conforming to the old pipe. This technology is ideally suited where larger diameter watermains need to be renewed and where the cost of open-cut (trenching) is a significant consideration. The City of Toronto is expecting to expand its structural lining program.
The City is currently undertaking a water loss reduction study. The study is assessing the benefits of implementing a number of operational and maintenance practices including: proactive leakage detection and repairs and pressure management which will have positive impact on reducing watermain breaks.
Watermain Break Reduction Study:
In 2005, the city investigated watermain breaks throughout Toronto in order to determine the causes of breaks, and potential prevention methods. The City is implementing recommendations from this study.
Responding to watermain breaks
When a complaint is received, Toronto Water staff are dispatched to determine the location and severity of the watermain break. Staff will isolate or close the effected watermain to stop the flow of water. Any property owners affected by the watermain closure will be notified regarding the closure and repair schedule. Staff will then excavate to expose the broken watermain and clean and dewater the area surrounding the break. Depending on the severity of the break, the watermain may be repaired by using a repair clamp or by replacing the deteriorated section of pipe.