Wellesley Water Hardness & Quality Report (2026)

The Wellesley Department of Public Works (DPW) Water Division manages the municipal supply for Wellesley, Norfolk County, Massachusetts, serving approximately 30,000 residents across 10.7 square miles. Primary sources include ten town wells—four near Morses Pond and six along Rosemary Brook—plus purchases from the Massachusetts Water Resources Authority (MWRA). Treatment occurs at three facilities: the Morses Pond, Wellesley Avenue, and Longfellow Road plants for local groundwater, with MWRA water integrated post-treatment. Annual Consumer Confidence Reports are posted at wellesleyma.gov; contact (781) 235-7600 x3355 or dpw@wellesleyma.gov.

The local watershed encompasses Morses Pond and Rosemary Brook drainage basins within the Charles River watershed, while MWRA sources originate from the Quabbin and Wachusett Reservoirs in central Massachusetts. Local groundwater interacts with glacial deposits and underlying metamorphic bedrock—including gneiss and schist of the Milford-Dedham zone from the Proterozoic Z and Cambrian periods—leaching calcium and magnesium from limestone and dolomitic lenses to yield a hard supply. Reservoir water contacts granitic and sedimentary formations, producing a moderately mineralised character that moderates the overall blend.

Wellesley's hard water promotes limescale buildup in pipes, heaters, and fixtures, with hot water heaters, dishwashers, and washing machines experiencing efficiency losses up to 50% from mineral deposits; soap lathers poorly, leaving films on skin, hair, and dishes. A traditional ion-exchange water softener is recommended for whole-house protection; salt-free systems offer scale control but do not fully soften. PFAS monitoring shows variability: 2022 Morses Pond at 45.1 ppt (above MassDEP 20 ppt MCL), though June 2023 non-detect; ongoing filtration has been installed. pH is adjusted via potassium hydroxide, fluoride totals 0.7 ppm, and disinfection is by sodium hypochlorite.