Charlestown Water Hardness & Quality Report (2026)

Charlestown, Massachusetts, in Suffolk County — the historic Boston neighborhood on the Charlestown Peninsula between the Charles River and Boston Inner Harbor, home of the USS Constitution (Old Ironsides — the world's oldest commissioned warship still afloat), the Bunker Hill Monument, and one of the most historically significant sites in the American Revolution — receives its municipal water from the Massachusetts Water Resources Authority (MWRA), which draws from Quabbin Reservoir (on the Swift River in central Massachusetts) and Wachusett Reservoir (on the Nashua River in Worcester County) through the MWRA's 18-mile Cosgrove Tunnel aqueduct system serving the Boston metropolitan area.

The moderately hard 121 mg/L hardness and TDS of 321.4 mg/L are harder than expected for the MWRA system — the Quabbin Reservoir is famously soft (typically ~15-30 mg/L hardness directly from the reservoir). The higher 121 mg/L at Charlestown likely reflects the MWRA's finished water after corrosion control treatment (the MWRA adds lime and orthophosphate for lead/copper rule compliance — alkalinity addition hardens the finished water significantly from the raw 15-30 mg/L Quabbin baseline). The MWRA corrosion control treatment (lime softening at the Carroll Water Treatment Plant) raises finished water hardness to approximately 100-130 mg/L throughout the Boston distribution system.

At 121 mg/L, Charlestown's water is moderately hard (from treatment, not geology) — scale builds slowly in kettles and appliances, dishwashers benefit from rinse aid, and faucet aerators need periodic cleaning. Quarterly descaling is appropriate. The PFAS level of 11.5 ppt is very high and warrants a certified reverse osmosis drinking water filter — Hanscom AFB (Bedford-Concord MA — a documented AFFF user in the MWRA watershed area), the Massachusetts Military Reservation (Cape Cod — significant PFAS plume), General Dynamics Electric Boat and the broader Boston-metro military-industrial PFAS complex all contribute to the MWRA's elevated PFAS readings.