Arlington Water Hardness & Quality Report (2026)

Arlington, Massachusetts, in Middlesex County northwest of Boston — a dense, highly educated Boston inner suburb between Cambridge and Lexington (one of the most affluent and progressive suburban communities in Massachusetts), home of a significant Greek-American and Armenian-American population, and a major MBTA commuter community on the Cambridge–Lexington corridor — draws its municipal water supply from the Quabbin and Wachusett Reservoirs via the MWRA. Water hardness in Arlington measures 77 mg/L — classified as moderately soft.

Arlington's moderate softness — harder than the MWRA source water but softer than downtown Boston neighborhoods — reflects the MWRA distribution infrastructure's mineral accumulation in the Arlington distribution zone. The MWRA Quabbin and Wachusett source water is very soft (typically 20–40 mg/L from the calcareous-poor Precambrian–Ordovician granite and gneiss watershed). Arlington's distribution infrastructure includes water mains from the 1910s–1950s dense inner suburb buildout era, accumulating moderate mineral content from the soft source supply. The moderate age Arlington mains produce the soft 77 mg/L.

With hardness at 77 mg/L, Arlington residents enjoy moderately soft water. MWRA consistently delivers water meeting all Massachusetts MassDEP and EPA Safe Drinking Water Act requirements.