Boston’s tap water is considered safe to drink and is consistently rated among the best in the United States. The Massachusetts Water Resources Authority (MWRA) manages the system and maintains a strong record of compliance with state and federal health standards. The water quality is generally excellent before it reaches the local distribution pipes. The primary concern for residents is not the municipal supply itself, but the condition of the plumbing within older buildings, which can affect the final quality at the tap.
The Source of Boston’s Drinking Water
Boston’s water supply originates from an extensive and protected watershed system located far west of the city. The two main sources are the Quabbin Reservoir, situated about 65 miles west of Boston, and the Wachusett Reservoir, located about 35 miles away. These reservoirs provide hundreds of millions of gallons of water daily.
The exceptional quality of the source water is due to extensive protection measures in the surrounding watershed lands. Over 85% of the land surrounding these reservoirs is covered in forest and wetlands, and approximately 75% of the total watershed land is protected from development. This natural filtration helps keep the water clean before it enters the treatment facilities, significantly reducing the processing required. Daily patrols and frequent testing of the streams and reservoirs are conducted to ensure the integrity of this water system.
System-Wide Quality Assurance and Treatment
The water treatment process is overseen by the MWRA and involves multi-step procedures designed to exceed regulatory standards. Water from the Wachusett Reservoir is treated at the John J. Carroll Treatment Plant. Primary disinfection is achieved using both ozone and ultraviolet (UV) light, which effectively inactivate pathogens like Giardia and Cryptosporidium.
The system also includes a sophisticated corrosion control process to minimize the leaching of metals from pipes into the water. This is accomplished by adjusting the water’s alkalinity and pH levels. Finally, a long-lasting disinfectant called mono-chloramine is added to protect the water quality as it travels through the local pipelines. The MWRA conducts over 2,000 community samples per month, monitoring for more than 120 potential contaminants to ensure continuous compliance.
Addressing Specific Contaminant Concerns
Lead and emerging contaminants are addressed by the MWRA with targeted strategies and consistent monitoring. Lead contamination is not an issue with the water leaving the treatment plants, as the source water is lead-free. The risk arises from private service lines and internal plumbing within older homes that may contain lead materials.
The MWRA’s corrosion control treatment, using chemicals like sodium carbonate, is designed to create a protective coating inside pipes to prevent lead from dissolving into the water. This strategy has been highly effective, reducing lead levels in high-risk homes by nearly 90% since 1992. In 2024, the 90th percentile lead level in targeted high-risk homes was below 6.9 parts per billion (ppb), well under the Environmental Protection Agency’s (EPA) action level of 15 ppb.
Another concern is the presence of Per- and Polyfluoroalkyl Substances (PFAS). Due to the protected nature of the watersheds, testing of MWRA-supplied water shows only trace amounts of these compounds. The sum of the six PFAS compounds regulated by Massachusetts is consistently zero, falling well below the state standard of 20 parts per trillion (ppt). The system already meets the new, stricter EPA standards announced in 2024.
Local Plumbing and Home Infrastructure Risks
The final stage of delivery—your home’s plumbing—is where water quality can sometimes degrade. Water quality issues can arise after the treated water leaves the municipal main and enters an older private service line or internal pipe. The corrosion of lead solder, brass fixtures, or a private lead service line can introduce lead into the drinking water, especially when the water has been sitting stagnant for several hours.
Residents can mitigate this risk, particularly if they live in a building constructed before 1986, when the use of lead solder was banned. Flushing the tap is the simplest action: running the cold water faucet for 15 to 30 seconds, or longer if a lead service line is present, clears out standing water. To determine if a property has a lead service line, residents can contact the Boston Water and Sewer Commission (BWSC) for records. The BWSC also offers incentive programs for replacing private lead service connections.