Flint, Mich., is not the only city with lead pipes — and an ever-present risk of toxic contamination in drinking water.

Pretty much every American home built before 1930 was constructed with a lead pipe to carry water from mainlines under the street into the tubs, toilets and faucets inside — a legacy that now haunts the 100,000 citizens of that largely poor industrial town.

But unlike Flint, cities in Minnesota and most other places manage that plumbing heritage through a strict regimen of regulation, chemistry and monitoring.

Which is why water plant operators in the Twin Cities say they are shocked by what happened in Flint. There, thousands of residents have been exposed to unsafe drinking water for close to two years since a switch in water sources and treatment facilities introduced a supply that stripped lead from underground pipes, contaminating the water indefinitely. It’s a major failure in public health that has drawn international attention and sparked lawsuits, investigations and resignations.

Those same risks are managed by watchful water treatment operators in every community that has older homes and older water delivery systems, allowing most residents to take safe water for granted.

“We are protecting people from pipes that they don’t even know could be bad for them,” said Rick Wahlen, manager of utility operations for Eden Prairie.

Like many newer communities, Eden Prairie doesn’t have a problem with lead, say state water treatment officials. But older cities such as Minneapolis and St. Paul do, if the homes and water systems haven’t been updated with copper. And many have not.

For them, protection has mostly taken the form of regulation and water treatment.

In the early 1990s, the U.S. Environmental Protection Agency (EPA) issued a rule under the Safe Drinking Water Act requiring cities to hold lead concentrations below 15 parts per billion, the level considered safe for infants and adults. In Minnesota, the first subsequent round of testing found that nearly 12 percent of the state’s community water systems exceeded that level. But they were still far below some of the extremely high levels recently found in Flint.

Since then, some local governments, such as the city of St. Paul, have been replacing lead pipes with the new standard, copper. Since the early 1990s, St. Paul has reduced the number of residential lead service lines from 30,000 to about 12,000, said Steve Schneider, the city’s director of regional water services. Whenever the city is doing street work or water main work, it uses the opportunity to replace lead pipes as well, he said.

But for most places the solution is chemistry. Cities use a combination of products that balance the acidity of the water so it does not corrode the pipes, along with others that chemically sequester the lead from water. When it’s all working correctly, the chemicals create telltale slick black biofilm that coats the inside of the pipes.

“It’s something we do pay a lot of attention to,” said Schneider. “We want to make sure our water is noncorrosive.”

In Minnesota, all community water systems regulated by federal law now meet the lead standard, according to the Minnesota Department of Health. The one alarm bell this year sounded in the small town of Nerstand, which found during a regular in-home survey that one home had high lead levels, which turned out to stem from a problem hot water heater.

In fact, Flint’s failure to provide what water treatment operators consider basic protection has left many of them scratching their heads.

“It absolutely floors me that someone … would ever let a system be supplied by water that is not stabilized,” said Wahlen.

But that is apparently what happened — an event so egregious in the public health world that last week it incited the resignation of Susan Hedman, director of the EPA region that includes Michigan and Minnesota. Agency officials said she and her staff did not act forcefully enough when they were told in April that Flint was not properly treating its water for corrosion. It wasn’t until Oct. 16 that the EPA established a task force to provide technical help.

By then, the damage was done. Doctors were reporting that children had high levels of lead in their blood and that the residential water pipes were stripped of their critical protections. Today, other than drinking bottled water, there is no solution in sight for Flint’s 100,000 largely African-American residents, many of whom live below the poverty line.

This week, environmental and religious groups said they intend to file a lawsuit and demand that all of the residential lead water pipes be replaced at no cost to residents.

If the shockwaves from Flint were to eventually result in a new federal standard outlawing lead pipes everywhere, it could cost taxpayers and homeowners billions of dollars, said Wahlen. But, he added, it wouldn’t surprise him if that were the outcome.

“To think that these people in Flint, day after day, believed their water was safe,” he said. “They must have tremendous feelings of distrust about their leadership.”