Because increased development poses a threat to Cambridge's water supply, State Sen. Michael J. Barrett '70 (D-Cambridge) said yesterday he is seeking to amend a Massachusetts water protection bill to include two city reservoirs.

Barret said he hopes to incorporate the city's main reservoirs at Hobbs Brook and Stony Brook into the Watershed protection Act. As it stands, the bill would only protect water supplies for Boston.

The act would create a 700-foot limited development zone around reservoirs to reduce the risk of contamination.

Barrett said he wanted a virtually identical bill, rejected last year, to include Cambridge but was advised that the change might prevent it from passing.

"I said fine, but next year when we start fresh, we're going to upset the applecart, and we're going to insist on Cambridge's inclusion," Barrett said.

The City Council unanimously endorsed Barrett's plan on Monday.

Cambridge's water supply has a history of contamination, according to Water Superintendant James J. Cusack, Jr. The level of sodium in city water is 43 milligrams per liter--more than double the 20 milligrams per liter limit set by state law.

But University Health Services director Warren E. Wacker said that figure is not high enough to pose a serious health hazard.

Cusack said the problem is caused by salt drainage running into the reservoirs from neighboring highways.

Several developments near the two reservoirs could pose an additional threat to the water supply, Cusack said, citing sanitary landfills in the nearby towns of Weston and Lincoln and a gasoline storage facility in Waltham as potential sources of contamination.

Cambridge finds it difficult to solve these problems because both reservoirs are outside city limits, Cusack said.

"Our built-in problem is that even though we maintain reservoirs, they're not within our jurisdiction," said Cusack.

Since Cambridge would be forced to draw on other water supplies in the event of a shortage, Barrett said his amendment was also important to the greater Boston area. He added that extremely low levels of precipitation this winter made a shortage likely.

"You are going to see declarations of water emergency throughout Massachusetts this summer," said Barrett. "[The Massachusetts Water Resource Authority] has a real investment in helping Cambridge protect its water supply so that we don't poach theirs."