Lead problems with the water in Flint, Mich., have prompted people across the country to ask whether they or their families have been exposed to the toxic metal in their drinking water, too.

When it comes to assessing the risk, it's important to look in the right places.

Even when municipal water systems' lead levels are considered perfectly fine by federal standards, the metal can leach into tap water from lead plumbing.

Kate Gilles moved to Washington, D.C., from Rhode Island for a job in international public health six years ago. When she was pregnant with her son, now 3, and her daughter, who turned 1 in July, she says she paid close attention to her health.

She ate better. She exercised. She followed her doctor's orders. Gilles checked off every task on the long list of things that she was supposed to do to help protect her babies.

But that was before Flint, and it never occurred to her to test her drinking water for lead.

No one — not her pediatrician, not authorities at her local water utility and not the realtor who sold her the home she lives in — suggested that she might have a problem with lead.

In April, she learned that her home is one of more than an estimated 6 million in America that gets its water delivered through a lead service line.

When There's Lead Underground

When there is a problem with lead in drinking water, service lines are the most likely culprit. Service lines are like tiny straws that carry water from a utility's water main, usually running below the street, to each building.

In older cities, many of them in the Midwest and Northeast, these service lines can be made of pure lead.

Wherever lead service lines are in place, there is a risk of water contamination. The toxic metal can leach into the water whenever something jostles the pipes, like nearby construction, a heavy truck coming down the road or when the water just sits still for too long.

Civil engineer Marc Edwards, the Virginia Tech professor who helped document the lead problems with water in Flint, calls lead service lines "ticking time bombs."

The Risks Of Low-Level Lead Exposure

Dr. Bruce Lanphear has spent decades researching low-level lead exposure, and his work is often cited by the Centers for Disease Control and Prevention. He says that while blood lead levels have been reduced drastically in recent decades, even levels as low as 5 micrograms per deciliter can lower IQs and increase the risk of attention and behavioral problems in children. For adults, lead exposure can cause kidney problems and high blood pressure.

Because it would be unethical to expose people to a known toxin, clear data are lacking on exactly how much lead a person must be exposed to before it shows up in the blood or triggers health and behavioral problems. Public health officials say that removing all lead from a person's environment is the best course of action.

Wherever lead service lines or other lead plumbing fixtures exist, there are precautions people can take to protect themselves — if they know they are at risk. They can flush their pipes every morning. They can purchase a filter certified for lead removal. Ultimately, they can replace lead service lines and lead plumbing in the house, though those replacements can be costly.

Still, there aren't any federal notification laws for the presence of lead plumbing as there are for lead paint. Checking the service line isn't part of typical home inspections. Landlords aren't required to warn tenants about lead pipes, and realtors don't need to tell potential buyers.

Gilles, who has a master's degree in public health, said she felt silly for not looking into lead risks from pipes. "But I also feel really angry that there's nothing that flags it for homeowners," she says.

Lead Regulations: 'Illusion Of Safety' Or Protection?

After learning that her house has lead pipes, she ordered a test kit from DC Water, the local authority. When she got the results, she was more confused than relieved. The test showed 0.7 parts per billion of lead in the water, far below the EPA's so-called action level, set at 15 parts per billion.

But what did the results mean? "I'm marveling at the total lack of lucidity of this letter," she says. "Because it doesn't say whether or not we need to be concerned. I'm guessing that the EPA decided that the margin of safety was this 15 parts per billion, and we're under that."

Except that isn't at all what the EPA decided.

The EPA seeks to control lead in the drinking water with its Lead and Copper Rule, created in 1991. The rule says that, depending on factors like how big a city is and how long it has been since high lead levels were last detected, water utilities have to test the water in between 50 and 100 homes with lead service lines every six months to nine years.

If 90 percent of homes have lead below the 15 parts per billion action level, the water utility passes the test. Nothing has to change. If the utility fails the test, it has to take follow-up action, including more testing and possibly changing water treatment methods.

But, critics say, there are several problems with the EPA's rule. For one, the most severe cases are essentially tossed out of the utilities' reports.

Also, according to the EPA's own research, the current lead sampling protocol requires water be collected immediately after the water has been stagnant for six hours. That means they are likely capturing the water that has been sitting inside the house, rather than the water that has been sitting in the lead service line. In other words, the utilities aren't capturing the full extent of the problem.

In addition, critics say, the EPA's trigger for action — or so-called action level — is set too high, at 15 parts per billion of lead in the water. Too many test results above that threshold are a red flag for water utilities, a sign that they might have a lead problem.

The number is often cited as a threshold for public health, but no amount of lead is considered safe for human consumption.

Jeff Cohen helped develop the EPA's Lead and Copper Rule back in the late '80s. He says that the action level didn't come from medical research; it came from water utilities.

"It was based on the little data that was available at that time from water utilities in the U.S. that had installed different levels of corrosion control treatment," he says.

Cohen points to the goal written into the rule, which is zero lead in drinking water. The action level, he says, is "not really designed to identify a safe level of lead in drinking water. It's simply one of many pieces of data that should be used to determine whether corrosion control treatment is working or not."

In June, the American Academy of Pediatrics called on federal regulators to tighten lead oversight, including lowering the action level. The Academy claimed that lead thresholds are set too high, they aren't based on science, and they create an "illusion of safety." Dr. Lanphear was the lead author on the AAP policy.

"We've consistently said that no level of lead is safe," says Joel Beauvias, the deputy assistant administrator for the EPA's Office of Water. He said that the 15 parts per billion action level isn't meant to be a threshold for public health.

The Safe Drinking Water Act says that the rule has to be updated every six years. The agency has been discussing possible revisions since 2010 and is looking at making improvements to the rule. But an agency spokesperson said it is too early to speculate on exactly what the agency will propose or when.

While the ultimate fix would be to replace all lead service lines and lead plumbing, that's a daunting task. In the meantime, there is a call for greater transparency about where lead service lines are in use so that people can reduce their risks.

The EPA wrote governors in February across the country encouraging, but not requiring, disclosure.

After multiple inquiries from NPR, D.C.'s water utility published a map of the lead service lines it knows about. The map is incomplete; there are more than 13,000 homes on the map that may or may not have lead pipes. Still, the map gives residents — particularly renters — easier access to the utility's records. In most cities, the information is still considered private and available only to the person paying the water bill.

George Hawkins, the general manager for DC Water, said it is in everyone's best interest to make lead service line inventories public. The information helps homeowners manage risks in the short term and can encourage them to replace lead service lines.

Although lead levels have gone down significantly in D.C. since the 2004 crisis, the majority of homes the utility has tested in recent years have still shown small amounts of lead in the water — 1 or 2 parts per billion.

Hawkins says that might be a problem for certain households. "Were I [in] a household with a wife who was pregnant or small children, I'd want that number at zero or as close to zero as it can be," Hawkins said.

Gillis decided that even small amounts of sporadic lead release weren't OK for her two children. She and her husband decided to have their lead service line replaced in May. It cost them $1,400.

She's had both of her children tested for lead and is reassured by the results. But she's still angry that no one told her about the lead service line — or the potential risk — earlier.

"The argument can be made that the onus was on us," she says. "But we didn't even know to look at it. This should really be the duty, the responsibility of the government."

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