Councilor: expansion tanks may cause water-meter overreads; city urged to notify residents

Councilor Ewen Kampen told the Somerville City Council on Tuesday that he has received multiple constituent reports alleging that home water meters can over-register usage when an expansion tank is installed on a household plumbing system and no check valve is present.

Kampen described a recent case in which a resident, an engineer who tested the matter, ran an independently validated flow meter in parallel with the city meter and found the city meter read about 19% more water over a month while an expansion tank was active. The resident then turned off the expansion tank and saw the difference fall to 4%; after installing a backflow preventer (a one-way check valve), the two meters read the same, according to the summary Kampen read to the council. "So, case closed," Kampen said while summarizing the resident's experiment.

Kampen said he and other affected residents sought guidance from city departments and were sometimes told the issue did not exist or that alleged improper work was at fault. He said inspectional services later told him the devices (check valves/backflow preventers) are required by code for installations involving expansion tanks. "That would be a very helpful piece of information at any point over the last several months," Kampen said.

When Councilor Wilson asked whether the city has instructions on how residents should proceed, Kampen said he did not have a step-by-step process and that some cases may involve work performed without required permits. He urged a plain public notice: if you have an expansion tank, have a plumber confirm the installation includes the appropriate check valve, or you may experience billing irregularities.

The council accepted the communication. Councilors emphasized they want clear guidance that residents can share with plumbers and neighbors; several said they would refer constituents to inspectional services pending an official public notice.