Ontario's water supply systems peaked at an average age of 21.2 years in 1987. New investments have brought down the age of this asset to 13.1 years in 2007, the lowest level since the 1960s. The rejuvenating trend was most pronounced from 2001 to 2007 when gross stock grew 7.1% a year on average, compared with about 5.1% at the national level. Only British Columbia recorded a faster stock growth rate (+8.1%). As a result, the share of this asset in Ontario's total public infrastructure stock increased from 9% in 2001 to 12% in 2007, the third most important investment after roads and highways and sewer systems.
As a percentage of estimated useful life, Ontario rate was above the national average through the 1980s and 1990s. This has changed in recent years. In 2007, water supply systems in Ontario had passed only 36% of their estimated useful life, compared with a national average of 40%.