Mayor Lori Lightfoot put the brakes on Chicago’s aggressive water meter program last month after another round of city testing found spikes of brain-damaging lead in more than 1 in 5 metered homes sampled, the Chicago Tribune has learned.

The decision by Lightfoot comes after five years of denials by former Mayor Rahm Emanuel that the nation’s third-largest city has a widespread problem with lead in drinking water.

Chicago continued to install water meters under Emanuel even after two of his top aides revealed they had known since June 2018 that a city study had found high concentrations of lead in several homes where the work has been conducted in recent years.

Shortly before Lightfoot took office in May, a state appeals court revived a lawsuit filed on behalf of residents seeking to force the city to dig up lead service lines, which Chicago required by law in single-family homes and small apartment buildings until Congress banned the practice in 1986.

The new mayor hasn’t decided if the city will fight the lawsuit as vigorously as Emanuel did. But she ordered city workers to stop installing water meters after aides briefed her about the ongoing study of lead levels in tap water.

“Out of an abundance of caution, Mayor Lightfoot decided to take immediate action upon reviewing the latest information,” Randy Conner, the city’s water commissioner and an Emanuel holdover, said in an interview Monday.

Of 510 homes tested since 2017, 22% had elevated lead levels in tap water after a meter installation, Conner said. About 7% saw lead levels spike higher than 15 parts per billion — three times greater than the Food and Drug Administration’s standard for bottled water.

Though the city declined to provide detailed results, a spreadsheet posted on a water department website shows how lead levels can vary widely among homes and depending on when water is drawn from a specific home.

One of the samples taken from a metered home in the Roseland neighborhood on the South Side contained a whopping 140 ppb of lead. On the North Side, water from a Rogers Park home contained 6.6 ppb of lead in the first liter collected, 14 ppb after the water had been running for four minutes and 24 ppb two minutes later.

City officials have known for decades that lead service lines are a public health hazard. They largely avoided scrutiny over the years by adding chemicals to the municipal water supply that form a protective coating inside lead pipes connecting homes to cast-iron street mains.

In 2013, experts from the U.S. Environmental Protection Agencystudy of Chicago homes published a detailing how that protective coating can break down if water hasn’t been used for several hours, allowing bits of lead or microscopic particles of the toxic metal to leach into tap water.

The researchers also found that lead levels in tap water could spike for months — or even years — if service lines had been disturbed by street work or plumbing repairs, including the installation of water meters.

Emanuel had dramatically expanded that type of work after taking office in 2011. His administration borrowed more than $481 million for water conservation projects, including the installation of household meters. The city raised water rates to pay back the 20-year loans.

Though the city water department participated in the EPA study, top Emanuel administration officials downplayed the results and insisted that Chicago tap water was still safe to drink. At one point, the Chicago Tribune reported in 2016, the city removed all references to lead in brochures distributed to residents before crews dug up streets or installed water meters.

Asked why the city failed to take action six years ago, Lightfoot’s acting health commissioner said officials needed more proof.

“The EPA study was just one piece of evidence,” said Dr. Allison Arwady, who served as the city’s chief medical officer under Emanuel and took over as health commissioner after Dr. Julie Morita stepped down in June. “We wanted to understand how concerned we should be about this.”

Lead is unsafe to consume at any level, according to the EPA and the U.S. Centers for Disease Control and Prevention.

Ingesting tiny concentrations can permanently damage the developing brains of children and contribute to heart disease, kidney failure and other health problems later in life. Researchers estimated in 2018 that more than 400,000 deaths a year in the U.S. are linked to lead exposure.

The chief source of exposure is dust from crumbling lead-based paint in homes built before 1978. But the recent water crisis in Flint, Mich., drew national attention to the lingering danger of lead service lines in older U.S. cities.

There is no federal standard for the amount of lead in tap water from individual homes. Utilities are considered to be in compliance with EPA regulations as long as 90% of the homes tested have lead levels below 15 parts per billion, a standard the EPA set nearly three decades ago because the agency thought it could be met with corrosion-inhibiting chemicals.

Chicago conducts this type of testing in just 50 homes every three years — the minimum required. Most are owned by water department employees or retirees living on the Far Northwest and Far Southwest sides, where cases of lead poisoning are rare.

By contrast, results from free testing kits — provided by the city upon request — show that lead-contaminated water has been found in at least one home in all 77 community areas.

Between January 2016 and March 21 of this year, more than 8,400 kits had been analyzed. Tap water in 13% of the homes sampled had lead concentrations above 5 parts per billion, the maximum allowed in bottled water by the FDA, according to a Chicago Tribune analysis.

Samples from nearly 1 in 5 homes had elevated concentrations of lead after the water had been running for three minutes, the newspaper’s analysis found. Even after water had been running for five minutes, 6% of the homes tested had lead levels exceeding the FDA’s bottled water standard.

City officials didn’t acknowledge the hazards until November, when the water and health commissioners held a hastily assembled news conference to announce they were offering free pitchers and six filters to all 165,000 homes with water meters.

The commissioners revealed they had known for six months about elevated lead levels in many of the metered homes sampled by city workers, prompting an outcry from aldermen and some of the candidates who were seeking to replace Emanuel.

“It’s dangerous, it’s irresponsible and it’s unacceptable,” Ald. Chris Taliaferro, 29th, said at the time.

Arwady, the acting health commissioner, noted that cases of childhood lead poisoning in Chicago have been steadily declining for years.

“This isn’t a public health crisis,” Arwady said. “But there are some steps people can take to reduce their chance of exposure to lead in drinking water, including using a filter and flushing their taps for at least five minutes if water hasn’t been used for several hours.”

In response to questions from the Tribune, Conner revealed that 8,000 water meters were installed during the past year, including 1,745 after he and Morita held their November news conference.

Only 10% of the homes eligible for free water filters have responded to the city’s offer, in part because of a limited public outreach.

mhawthorne@chicagotribune.com