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Watershed FAQs

Watershed Frequently Asked Questions

• Where does my water come from?

  Cambridge water comes from the Stony Brook Watershed, nested in the Charles River Basin, in the towns of Lincoln, Lexington, Weston, and the City of Waltham. The water makes its way by gravity through a series of tributaries, reservoirs, and pipes to Fresh Pond in Cambridge, where it is pumped into the Walter J. Sullivan Purification Facility for treatment. The finished water is pumped to and stored in the underground Payson Park Reservoir in Belmont, where is it fed by gravity to the residents and businesses of Cambridge.

  Learn more in Where Does Our Drinking Water Come From

• What does "watershed" mean?

  A watershed is a region in which all water (stream and ground water) flows to the same point.

• How was Fresh Pond formed?

  The Fresh Pond Reservoir is a "kettle" pond, which formed after the last glaciation of New England. Kettle ponds form by large blocks of ice that have broken off of the receding glacier. These blocks slowly melt in the glacial till and sediment-rich outwash left by the glacier and form shallow depressions that later fill in with precipitation and groundwater. Kettle ponds have no natural surface inflows or outflows.

• Should I be worried about the roads and businesses surrounding Fresh Pond?

  No. In order to reduce the inflow of polluted urban runoff, Fresh Pond's 1,297 acre topographical watershed has been restricted to only the reservoir and a narrow border within the Fresh Pond Reservation by intercepting and redirecting local drainage around the reservoir to Alewife Brook.  Under normal operating levels, most of the water in Fresh Pond comes from the upper watershed, with only approximately 7 - 11% of average daily demand from its small overland drainage plus groundwater flows from the Fresh Pond watershed.