Drinking water in Cambridge will be back to the city’s own supply starting Saturday. (Photo: Karolina Grabowska via Pixabay)

Cambridge goes back to using its own drinking water supply Saturday, City Manager Yi-An Huang said Thursday.

It switched to getting drinking water from the Massachusetts Water Resources Authority system on Aug. 30 because of rising levels of a worrisome group of chemicals known as PFAS in the city’s own water supply. Supply chain problems had delayed installation of new filters designed to remove more of the chemicals as health guidelines got stricter, the city said.

Since then the Water Department has installed granular activated carbon filter media at its Walter J. Sullivan Water Treatment Facility that is proven to remove the worrisome compounds from water, Huang said in a press release, and “as a result, the current PFAS6 levels in the treated water from city-owned water reservoirs are now equivalent to the MWRA water quality.”

“Massachusetts has some of the strictest PFAS standards in the country, and the City of Cambridge is committed to providing high-quality water to our community,” Huang said. “My children and I continue to drink our city’s tap water with confidence.”

Before the installation of the GAC filtering, the chemical level was 17.1 parts per trillion, and it is now under 5 ppt with only two of the six filters completed, the city said. The city expects continued reductions as the rest of the filters are installed over the next two months, said Sam Corda, managing director of the Cambridge Water Department. 

The temporary switch to MWRA water – which in August the city said would likely last until the end of the year – cost the city approximately $7 million, and the new filters cost $1.5 million, the city said.

Water travels from Hobbs Brook Reservoir to Stony Brook Reservoir and is pumped to Fresh Pond, where it’s stored before treatment at the plant next to Fresh Pond. Then the treated water is pumped to an underground storage reservoir at Payson Park in Belmont. From there it’s distributed by gravity to residences and businesses in Cambridge.

The city has monitored since 2019 for PFAS – a group of more than 1,000 chemicals used widely since the 1950s in a variety of products including food packaging, firefighting foam and nonstick coatings on cookware. They break down so slowly that they are known as “forever chemicals” and are found throughout the environment. 

Cambridge turning to the MWRA and its Quabbin Reservoir was last necessary during a 2016 drought, when the city’s water supply ran low.

Sue Reinert contributed to this report.