The Hobbs Brook Basin Gate House in Waltham. (Photo: Magicpiano via Wikipedia)

Cambridge has won a $1 million state grant to repair a gatehouse and dam outlet pipe that are part of the city’s drinking water supply system. The structures are at the Hobbs Brook Reservoir in Waltham.

The money from the Executive Office of Energy and Environmental Affairs will pay for repairing and repointing the granite block foundation and weir of the Hobbs Brook Gatehouse on Winter Street, city spokesperson Jeremy Warnick said. The city will also repair erosion and undermining of the Hobbs Brook dam outlet pipe, he said.

“This work will help reestablish full structural integrity and prevent potential erosion and/or future damage,” Warnick said.

Cambridge is suing over a 5.5-acre solar panel project in Lexington that would cut down more than 1,000 mature trees protecting the Hobbs Brook Reservoir, the main source of Cantabrigians’ drinking water.

Cambridge owns four reservoirs: Hobbs Brook in Waltham, Stony Brook in Waltham and Weston, Fresh Pond at the water treatment plant in Cambridge and the underground Payson Park in Belmont. Water flows from Hobbs Brook Reservoir to Stony Brook Reservoir, then via an underground pipe to Fresh Pond. After treatment, water is pumped to Belmont and distributed by gravity to Cambridge customers.

The Hobbs Brook Gatehouse, also known as the Winter Street Gatehouse, was built around 1897. Both the Hobbs Brook and Stony Brook reservoirs were created by dams in the 1890s. Fresh Pond is a “kettle pond” that has no natural inlets or outlets, according to the city’s Water Department.

The Hobbs Brook Gatehouse was last renovated in 2011-2012, when the city replaced manually operated cast-iron slide gates with new stainless steel, electrically actuated gates, Warnick said. During the next two years, the city repaired damage to the dam from storms in 2010.

The work that’s planned will correct problems identified in a Water Department inspection in 2021. The department performs comprehensive routine inspections every two years, as required by the state.

Warnick said the City Council, now in recess for the summer except for an Aug. 7 meeting, must appropriate the money before work can start. Work will begin this fiscal year, which ends next June 30, “assuming all goes well,” Warnick said.