Cambridge Water Hardness & Quality Report (2026)

Cambridge, Massachusetts — home to Harvard University and MIT — draws its municipal water supply from the Massachusetts Water Resources Authority (MWRA), sourcing from the Wachusett Reservoir on the South Branch Nashua River in Worcester County and the Cosgrove Reservoir system in northern Worcester and Middlesex Counties. MWRA delivers treated water to Cambridge and 60 other communities in the greater Boston metro area via the Cosgrove Tunnel and distribution mains. Water hardness in Cambridge measures 86 mg/L — classified as moderately soft.

Cambridge's moderately soft supply reflects the New England Uplands crystalline geology of the MWRA Wachusett watershed. The Wachusett Reservoir watershed drains the Massachusetts Uplands — terrain underlain by the Precambrian–Ordovician Nashoba Zone (Marlborough Granodiorite, Nashoba Formation biotite schist) and Ordovician–Silurian Fitchburg Plutonic Suite granites and granodiorites. These ancient siliceous crystalline rocks are thoroughly depleted of soluble calcium after Grenville-age and Taconic metamorphism, contributing minimal carbonate minerals to watershed drainage. MWRA's consistently high water quality reflects protected watershed management and state-of-the-art treatment at the John J. Carroll Water Treatment Plant.

With hardness at 86 mg/L, Cambridge residents experience minimal to moderate scale accumulation. Faucet aerators and showerheads develop deposits slowly — bi-monthly cleaning with citric acid solution is sufficient. Soap and shampoo lather well. Dishwashers produce clean glassware with moderate rinse-aid use. MWRA consistently delivers water meeting all Massachusetts DEP and EPA Safe Drinking Water Act requirements.