Back Bay Water Hardness & Quality Report (2026)

The Massachusetts Water Resources Authority (MWRA) supplies drinking water to Back Bay in Boston, Massachusetts, serving over 3 million people across 51 fully supplied and 49 partially supplied communities in Greater Boston. Water is primarily sourced from the Quabbin Reservoir (90% average) and Wachusett Reservoir (10% average), both in central Massachusetts. The Carroll Water Treatment Plant in Marlborough treats Wachusett water, while Quabbin water receives minimal treatment at the Quabbin distribution point. Back Bay receives this treated surface water via the MetroWest and Metropolitan tunnels.

The Quabbin Reservoir lies in the Ware River Watershed (Swift River sub-basin), and Wachusett in the Nashua River Watershed — both are protected forested uplands with strict no-development policies. Underlying geology features Precambrian and Ordovician metamorphic rocks, including Brimfield Schist and Paxton Schist formations, with no significant carbonate bedrock. This granitic-metamorphic terrain yields very soft water, as thin soils and fractured bedrock impart few dissolved minerals during infiltration, keeping the supply geologically soft with low dissolved calcium and magnesium.

Soft water causes minimal scale buildup, posing little risk to plumbing, appliances, or fixtures, and extends the lifespan of water heaters, dishwashers, and washing machines without frequent descaling. No water softener is needed or recommended; softeners would unnecessarily introduce sodium. Use standard cleaning products and monitor copper pipes for corrosion, though MWRA adjusts pH to 9.0–9.5 for stability. Lead and copper remain within EPA action levels; no PFAS detections above limits in recent tests; treatment at the Carroll Plant includes ozone, UV, and biological filtration; disinfection uses chloramine, with fluoridation included.