Belmont Water Hardness & Quality Report (2026)

Belmont Water Department (MWRA) serves approximately 25,211 residents in Belmont, Middlesex County, Massachusetts, receiving its entire supply from the Massachusetts Water Resources Authority (MWRA). The source is surface water from the Quabbin Reservoir, treated at the John J. Carroll Water Treatment Plant in Marlborough, MA. Distribution occurs via MWRA's metropolitan Boston conveyance system, with local management by Belmont's Water Division at 35 Woodland St. No local wells or groundwater are used; the supply is entirely purchased wholesale surface water sourced from the protected Quabbin watershed.

The Quabbin Watershed spans 120 square miles of protected forest in central Massachusetts, preserved since the 1930s reservoir impoundment. Underlying geology features hard, resistant metamorphic rocks — schist and gneiss — from Paleozoic Appalachian formations, with granitic intrusions over thin glacial till soils. Absent carbonate rock layers, the raw water exhibits a very soft character with low natural mineralisation and near-neutral pH around 6.8, prone to picking up pipe metals without treatment adjustment.

Soft water at 17.5 mg/L minimises scale buildup in pipes, heaters, and appliances — no limescale on fixtures or clogged showerheads; kettles and dishwashers operate efficiently. No water softener is needed or recommended; focus instead on regular pipe checks for corrosion, as soft water can be mildly aggressive to plumbing. MWRA adjusts post-treatment pH to approximately 9.3 to inhibit corrosion. Disinfection uses chloramines, hypochlorite, ozone, and UV; fluoride residual is 0.9–1.0 mg/L; all EPA MCLs are met, and lead monitoring shows levels well within compliance.