Columbia Falls’ water supply got a clean bill of health Wednesday.

On Thursday morning, the Montana Department of Environmental Quality officially lifted the health advisory that had been in place during November.

The first good news came after two successive sets of water tests showed no trace of the coliform bacteria that showed up the first week of November.

“We got the verbal confirmation that the test results are good,” Public Works Director Lorin Lowry said of the phone call he got from the testing lab.

“There were no detects,” or signs of contamination, he said. “We managed to cleanse our system. We’re in good shape.”

The Department of Environmental Quality then reviewed the lab results and concurred.

In November’s routine monthly testing, the DEQ found coliform bacteria in three out of five samples. The threshold is that no more than one sample a month may show contaminants.

Coliform bacteria themselves are not a health threat. Generally they are nothing more than an indicator that other potentially harmful microbes may have found their way into the water supply, but treatment still is required.

Lowry said street construction this fall and accompanying work on water lines probably introduced the contaminants.

On Nov. 9 Lowry’s department started a two-week regimen of chlorinating the city’s entire water supply.

They allowed a few days’ resting period after the chlorination stopped, then tested again on Nov. 24.

Those five samples all came back clean, he said.

On Tuesday they completed the official sampling process with December’s routine monthly testing. Lowry sent those samples to the lab along with a request for a phone call to let him know the results as soon as possible.

He got the good news at midafternoon Wednesday.

The DEQ’s health advisory — a heads-up to water customers, not a boil order — stayed in place through the end of November as a matter of policy.

“You’re on notice for the entire month,” Lowry said. “They won’t even reconsider until you draw your next routine samples. It’s critical to draw samples at the beginning of the month so you have time to work on it.”

All city water customers should receive a mailing in the coming days notifying them of the results.

Columbia Falls’ public water supply is not chlorinated or otherwise treated because of a series of safeguards implemented over the years. One was a wellhead protection zone established some time back and another is a more recent requirement for backflow prevention devices at all individual service lines.

When the city met the standards, and could show it draws its drinking water from a protected aquifer, the state granted a variance from the disinfection requirement.

More stringent groundwater rules kicked in on Tuesday, meaning the city has an even greater interest in keeping its water supply squeaky clean.

“They are EPA rules on operation of groundwater sources, all water systems including ground and surface water,” Lowry said.

Since the variance already was in place, the city was grandfathered in when the new regulations took effect Dec. 1.

“I don’t think we would get back on it if we have too many occurrences like this,” he said.

Reporter Nancy Kimball can be reached at 758-4483 or by e-mail at nkimball@dailyinterlake.com