Sanitary and storm sewers in Ontario reached their lowest average age during the 1970s at 14.2 years. Since then, their age has risen slowly, reaching a high of 18.4 in 2002, and then dropping marginally to 18.3 years in 2007. The slow ageing of this infrastructure can be linked to a combination of moderate investment rates over the years and low discard rates from the gross investment stock.
As a percentage of estimated useful life, Ontario has been slightly above the national average since the early 1980s. In 2007, the provincial rate was 54% compared to 53% nationally.