Although the outcry against trihalomethane (THM) levels in Cambridge water has quieted down since last spring, the city's water department has not abandoned efforts to improve Cantabrigians' water supply.

The Cambridge City Council last week approved a $950,000 water appropriation that will be used to maintain and upgrade the current purification system and also to plan for a major overhaul during the next few years.

According to Cambridge Water Superintendent John J. Cusack, Jr., one of the most important changes in the city's water process will result from a decision to switch from a purification system using liquid and gas chlorine to one using a chlorine compound called sodium hypochlorite.

Water officials say the chlorine conversion will aid Cambridge's much-publicized battle against THMs, which are known to cause cancer in certain laboratory animals. As recently as last December, THMs in Cambridge water exceeded the government-approved level of 100 parts per billion (ppb).

According to Cusack, THM levels have remained at around 40-50 ppb over the past three months. He credited the recent completion of a cover over the city's reservoir as a major factor in the improvement.

The change in the chlorine process will also make water purification safer, Cusack said. Earlier this month two workers were hospitalized after a one-ton tank of chlorine liquid burst.

Mayor Alice K. Wolf said concern among Cambridge residents about the chemicals had prompted her to question the size of the $950,000 appropriation. "I wanted to make sure we were doing enough [to maintain low THM levels]," she said.

"I'm satisfied that we're doing what we can for the moment," Wolf said, "but I won't stay satisfied unless we continue the pace."

However, Councillor Francis H. Duehay '55 said that he is "frustrated at the Water Board and Water Department's ability to work with the city." He added that communication problems between officials and citizens have not been addressed.

Last January, the Cambridge Water Department sent letters to customers notifying them that THM levels in the water from July 1988 through December 1989 exceeded Environmental Protection Agency limits. Duehay criticized the department for sending the letters a full six months after the first violation occurred, and also for the confusing wording used in the correspondence.

"Often the warnings are couched in technical language," said Duehay. "What they do is raise the level of concern."

Duehay has also questioned the department's decision to tell citizens of the water problems in their bills--rather than through a mass mailing to all residents. Duehay said that tenants in apartment buildings and university dormitories remained uninformed of the problems, a situation that he has tried to remedy.

"The city has been very good at reducing elements in the water and doing long-range planning," said Duehay. "[They] should not just send the required notes but [should also] explain the problem and what [they are] doing to improve. The public would have a great deal more understanding that the water is good and going to get better."

Cusack said that the transition to the new purification system would use up less chlorine and allow the city to store an "adequate stockpile" of the chemical indoors. He said the conversion should take six months to implement.

The second part of the conversion, which may take up to six or seven years to complete because of the guidelines and contracts involved, calls for "complete renovation or total replacement" of Cambridge's 68-year-old water system, Cusack said.