The Chicago water department’s efforts to conserve water by installing meters in homes citywide prompted anger from aldermen and others on Thursday after city officials revealed they’d known since June that a “small sub-set” of those homes had elevated lead levels after being tested.

The testing, quietly done by City Hall, found that 51 of 296 tested metered homes — 17.2 percent — had lead levels above the federal standard of 15 parts-per-billion.

Some 165,000 homes in Chicago have meters. So if 17 percent of them are impacted, that could mean 28,000 of them have elevated lead levels.

The water department had known about the results for roughly four months, but, until this week, hadn’t informed the general public. And only now is City Hall offering homeowners with meters free, $60 water filtration systems.

Speaking with reporters, Water Management Commissioner Randy Conner and Health Commissioner Dr. Julie Morita refused to say precisely how elevated the lead levels were — and initially refused to provide specific test results. The precise figures were provided after-the-fact by Mayor Rahm Emanuel’s press office.

City officials said they notified the 51 homeowners whose homes had tested positive for elevated lead levels immediately after getting the results. They also said the test results showed there’s no reason for panic.

Conner was asked why installation of water meters — which City Hall has been pushing for years to promote water conservation — has not been suspended in light of the results. “We’re still installing meters because the data that we have is showing a slight increase,” he said.

“When you look at the data here and you see the progress that’s been made, we’re not looking at a public health crisis,” Morita said. “This is a complicated, multi-year, multibillion-dollar endeavor and we want to do this right. So we took a pro-active approach in terms of looking at the water mains, the water meters and that information is now informing us to now look at the lead service line replacement.”

Thursday’s news conference had been called to announce Emanuel’s surprise decision to ask the engineering firm of CDM Smith to conduct a $750,000 study to evaluate the cost of and potential funding sources for a multiyear plan to replace the lead pipes running from the water mains to roughly 360,000 Chicago homes.

Conner acknowledged the study will not be done until spring, when Emanuel is scheduled to leave office and pass the multibillion-dollar political and public safety hot potato to his successor.

The test results about metered homes were announced as Conner and Morita tried to portray the study as evidence of the Emanuel administration’s stance on an issue of great concern in the wake of the water crisis in Flint, Michigan.

“Preliminary data indicates that a portion of a relatively small sample of homes that have had water meters installed reported increases in lead levels,” Conner said. “While more than 80 percent of homes did not have lead levels above the EPA action level after the installation of a meter, we know that one of the only remaining sources of lead is in the lead service lines.”

“Although the ongoing study is not yet complete, out of an abundance of caution, we have decided to take actions based on the preliminary data on water meters. These actions will include providing free water filter sets to any home that had previously tested above the EPA action level and to metered homes that request a filtered set.”

At that point, the news conference went south. Reporters demanded to know why all 165,000 homeowners with meters were not notified immediately of the shocking test results.

The city notified only the 51 homeowners whose metered homes had tested positive for elevated lead levels. That’s even though top mayoral aides have known since June that 11 percent of tested metered homes had elevated lead levels and found out Friday the figure was 17.2 percent.

“At the time, we were still getting the data in and taking a look at it along with myself, along with Dr. Morita and the scientists to come up with a decision on how we were going to approach the situation,” Conner said of the June results.

Morita added, “People should not be panicked. That is the critical message. And you can help us to do this by not making it a panic situation. When you look at the data, this should be very reassuring. . . . We have thousands and thousands of children that are tested annually and this number has continued to decrease over time.”

After sitting through the news conference, Ald. Gilbert Villegas (36th), chairman of the City Council’s Hispanic Caucus, was more determined than ever to bankroll replacement of all lead service lines with a one percent increase in the real estate transaction tax applied to homes sold for over $750,000.

“What are we doing here? Let’s get ahead of this thing. . . . Let’s stop burying our head in the sand,” Villegas said.

Ald. Scott Waguespack (32nd) branded the delay in notifying the owners of all metered homes “dangerous and unacceptable” and an invitation to a potential avalanche of lawsuits.

“Over 28,000 homes with the meters could have this potential lead poisoning. And this is poisoning. It’s not just a lead pipe that needs to be removed,” Waguespack said.

Ald. Chris Taliaferro (29th) said the Emanuel administration has blocked every resolution and ordinance introduced as a possible remedy to elevated lead levels in Chicago’s drinking water.

“We cannot allow this administration or this city to sweep this problem under the rug because, if we do, our city will be in danger as Flint has been,” Taliaferro said.