Nyack Water Department officials are unsure of what led to , and are continuing to look into the matter, they said.
"We don't know what caused it," said Michael Kaneletz, head of the Board of Water Commissioners of Nyack. "There are numerous possibilities. We're investigating and discussing it with our engineers."
Kaneletz said the —which indicate other, dangerous pathogens could be in the water supply—may have been from high water temperature.
"Hot weather might have exacerbated the problem," he said. "The water was warm, and warm things grow funky stuff."
Other causes could have been water spending too much time in storage tanks, or improper flushing. The Water Department does flushing about once a year in May, but used to do so twice a year.
"Perhaps it is time to go back to twice a year," Kaneletz said.
Due to the Water Department's routine testing schedule—15 tests a month—and a lag at EnviroTest Laboratories, the private laboratory that processes water samples, Nyack's water may have been contaminated for up to a week before residents were notified, Kaneletz said. The Water Department submitted a sample for testing under normal protocol on June 13, but did not hear back from the laboratory until June 17—usually, there is only a 24 hour turnaround.
"We had three days lag time," Kaneletz said, adding that negligence may have played a factor.
Ronald Bayer, a lab director at EnviroTest, said there was a delay because the laboratory was testing for things other than coliform.
"When we're doing [multiple tests] it takes 48 hours," he said. Bayer noted EnviroTest was looking for coliform, E. coli and other bacteria. The E. coli tests were negative, but coliform and other bacteria were found.
"We have no clue what caused it," Bayer added. "We just pick up the samples, test them and report on the data."
On June 17, when officials learned of the coliform level, they began another round of testing per protocol. In doing so they learned that water from two of six samples sites was contaminated, and the Rockland County Department of Health released a public message on Tuesday, June 21.
"I can't tell you how much [the public] was at risk," Kaneletz said. "I don't know if there was any risk. When we find an excessive amount of coliform, the horse is already out of the barn. What we do is take corrective action."
Kaneletz said such actions included an "aggressive flushing program" at six strategic locations, and introducing chlorine as a disinfectant. The next steps in tracking down the cause include studying water usage records and carrying out more tests, Kaneletz said.