Charlestown Water Hardness & Quality Report (2026)

Charlestown, Massachusetts receives its water supply from the Massachusetts Water Resources Authority (MWRA), which serves the greater Boston metropolitan area. The primary source is the Quabbin Reservoir in central Massachusetts, supplemented by the Wachusett Reservoir. Water is conveyed via the MetroWest Water Supply Tunnel to the John J. Carroll Water Treatment Plant in Waltham, where it undergoes ozonation, chloramination, and pH adjustment before distribution through approximately 4,000 miles of pipeline to over 3 million people across 51 communities.

The Quabbin Reservoir watershed spans 120 square miles of protected forest in the Swift River Valley, part of the larger Chickopee River basin within Paleozoic metamorphic terrains. The underlying geology features the Ordovician Brimfield Schist and gneissic formations with sandy glacial soils, absent significant carbonate rocks like limestone or dolomite. This resistant metamorphic bedrock imparts very little calcium or magnesium to the surface water, producing a very soft supply with low dissolved solids.

As soft water, Charlestown's supply produces minimal limescale buildup, posing little risk to plumbing, water heaters, or appliances. No significant spotting on dishes or reduced detergent efficiency occurs, and standard cleaning is sufficient. A water softener is unnecessary and not recommended. MWRA maintains pH at 9.0–9.5 to minimize lead and copper leaching, consistently meeting EPA action levels. PFAS levels are nondetect or below advisory limits, and treatment involves pre-ozonation, dual disinfection, and corrosion inhibitors for a reliably safe supply.