How You Get Your Water

The water Cantabrigians see when they turn on their tap travels a long way before reaching their homes and businesses, says Nancy E. Barnes, director of the Cambridge water department.

The water is collected in the Cambridge watershed, an elevated area of land west of the city, in Lincoln and Weston.

Rain water drains into a series of small ponds and streams and then flows into Cambridge's two primary water sources: the Hobbs Brook Reservoir in Lincoln and the Stony Brook Reservoir in Weston.

Water from the Hobbs Brook Reservoir spills naturally through streams and ponds into the Stony Brook Reservoir. From there, the water flows downhill in an underground pipeline to Cambridge, where it is collected at Fresh Pond.

Water from Fresh Pond is drawn into the Fresh Pond Water Treatment Plant. Once inside the Plant, water is mixed with alum, a coagulant, which combines with organic matter and settles to the bottom in sedimentation basins.

After the sedimentation process, water is strained through a filter basin containing and mixed with a carbon compound.

The filtered water flows through an aerator, which allows the water to mix with air. Barnes says the aeration process is the most important step in water treatment, because as water reacts with air many contaminants are eliminated.

"If I could develop the perfect water treatment process," Barnes says, "I'd use lots of aeration and almost no chemicals."

Still, chemicals are added to the water after the filtration process in accordance with EPA specifications.

Barnes says the water department currently adds fluorine for dental health and a mixture of chlorine and ammonia for purity.

After treatment, the water is pumped to the recently covered Payson Park Reservoir, which can store a maximum of 30 million gallons of water.

Water is dispensed from Payson Park in accordance with Cambridge's demand, and flows through city pipes to homes, businesses, and schools.