Water mains are the primary pipes in municipal water distribution systems, carrying treated drinking water through streets and neighbourhoods. Transmission mains are large-diameter pipes (often 400mm or larger) moving water in bulk from treatment plants and storage facilities. Distribution mains (typically 150-300mm) serve local areas, with service lines branching off to individual properties. Water mains are typically buried below frost depth to prevent freezing. Main materials include ductile iron, PVC, concrete, and historically cast iron or asbestos cement. Water main breaks can cause flooding, property damage, service interruptions, and boil water advisories. Aging water main infrastructure across Canada requires massive replacement investment. Main replacement is often coordinated with road reconstruction to minimize disruption and cost.