The results satisfied health officials that a more proactive monitoring system was not needed.

“We were never satisfied,” said Steve Kaufman, who was Mr. Sanders’s chief of staff at the time.

Insisting on Inspections

In 2009, at the urging of Mr. Kaufman, Daniel Garodnick, a city councilman who lives in Stuyvesant Town, sponsored legislation that would require the health department to track water tank inspections through a database.

The health department called the measure unnecessary and too expensive. Christopher Boyd, the director of the department’s Office of Public Health Engineering, told the Council the database would cost $300,000 to set up and $65,000 a year to maintain.

The Council decided against the database, but passed a bill mandating, for the first time, that building owners make inspection records available to tenants, and to post proof of the inspections in prominent places. It also, for the first time, required that tank water be tested for contamination once a year. The new law required the health department to conduct three surveys, checking the inspection records of 100 randomly chosen buildings each year from 2010 through 2012.

The results were not encouraging. No more than 42 percent of the buildings surveyed each year could provide proof of a bacteriological test. Of those buildings that could provide proof, all were found to be free of contamination, though the samplings were typically done after the tanks were cleaned, which is allowed. But even among these buildings, most failed to post their inspection notices, and most could not provide proof that they had performed an inspection in each of the previous five years, as city law also requires.

More than $700,000 in fines was levied against the buildings in the survey. Despite the findings, the health department said it had no plans to expand enforcement of the laws, though it said it would continue to do annual surveys.

“The department continues to monitor compliance with the regulation and improve compliance by consulting with building owners regarding the requirements, through Realtor associations and building management companies,” the department said in a statement.