The water crisis in Flint, Michigan, has cast a national spotlight on the threat posed by lead contamination in tap water. What happened in Flint is a worst-case scenario but is far from an isolated concern. Many people in Maine and across the U.S. drink water that flows through old pipes and fixtures that contain some lead.

USA Today reported last month that nearly 2,000 public water systems across the U.S. showed elevated lead levels since 2012. Over that same period, nearly 50 schools, water districts and other public water systems in Maine tested positive for high levels of lead.

Among those was the Bangor Water District.

In 2010, the water district discovered a spike in lead levels coming from the taps of area homes as part of routine lead and copper testing required by the U.S. Environmental Protection Agency. After tweaking the water chemistry, the lead levels are declining at a steady clip and the water district is back in compliance with federal lead regulations, according to Dina Page, water quality manager at the Bangor Water District.

Maine isn’t likely to see a Flint-like water crisis, but Mainers who live in homes with older plumbing are at a greater risk of lead exposure. That’s one reason water districts across the state continually keep an eye on lead levels — even if the pipes used to deliver water are lead-free.

Close to home

Floods Pond in Otis, where Bangor Water District draws its water, is lead-free. In fact, when lead turns up in the drinking water, it is very rarely from the source because, despite the fact that lead occurs naturally in the environment, most water bodies have very low levels of lead.

None of the 200 miles of pipes funneling water beneath Bangor contain any lead components.

“We’re fortunate that we do not have lead in our source water and our distribution system,” Page said.

The source of lead contamination, it turns out, is close to home: the plumbing.

Older homes built throughout much of the last century often were outfitted with pipes with lead-soldered joints and brass fixtures — such as faucets, valves and fittings — that contain lead. When water sits for several hours in contact with lead solder, the heavy metal begins to leach into the water.

If water has sat in pipes with lead components for several hours, run the water for two to three minutes before cooking or drinking to flush out any lead that may have leached. “My advice to people: Don’t drink stagnant water,” Page said. “Our pond isn’t going to dry up if everyone runs the water for two minutes.”

Since the 1980s, the federal government has taken measures to reduce the risk of lead exposure in drinking water. In 1986, lead solder was taken off the market after Congress banned its use. In 1991, under the lead and copper rule, the EPA mandated that public water systems test for lead contamination. Since 2014, federal law prohibits plumbing fixtures from containing more than 0.25 percent lead; previously, fixtures could contain up to 8 percent lead and still be advertised as “lead-free.”

Homes built since 1986 have almost zero risk of lead exposure.

Still, people living in older housing stock outfitted with older plumbing remain at risk. Even within one neighborhood, the level of potential lead exposure varies from one house to another depending on how much lead is in the plumbing.

For water district and public health officials, it is difficult to monitor and determine the level of lead exposure because the heavy metal commonly gets into the water only after it leaves treatment facilities, according to a 2009 report in the journal Environmental Health Perspectives.

So the Bangor Water District can do little other than continually assess whether its water chemistry and treatment process is adequate to ensure that residents of Greater Bangor have minimal risk of lead exposure.

Action level

When the Bangor Water District tested household taps for lead in 2010, it found that eight of 46 test sites had levels between 18 parts per billion and 60 parts per billion.

Before that, lead levels had only once reached the maximum accepted threshold of 15 parts per billion set by the federal government — in 2002. The water district has monitored lead levels since 1992, when the the lead and copper rule took effect.

Under the rule, at least 90 percent of households must have lead levels at or below 15 parts per billion. If too many households exceed the lead threshold, the water system must inform the public and take steps to reduce contamination.

This threshold, however, is a regulatory measure, not a health-based one, according to a 2011 report by the EPA Science Advisory Board. Ideally, the maximum level of lead contamination is zero. Rather, this threshold acts as a red flag for public water systems to adjust their treatment processes or replace lead service lines, if they exist.

No amount of lead is safe to consume. Even small doses are dangerous, especially for children and pregnant women. In children, lead can cause learning disabilities and behavioral problems, among other complications. Adults also can suffer health issues from lead exposure, including high blood pressure, kidney problems and cancer.

Based on the population it serves across seven municipalities, the Bangor Water District must monitor at least 30 households under the federal lead and copper rule. Page said the water district focuses on monitoring for lead in houses built between 1982 and 1986.

Houses built before 1986 are more likely to have plumbing with lead-soldered joints than those built after lead solder was taken off the market. But in houses built before the 1980s, the plumbing has likely built up a coating of minerals in the plumbing that acts as a buffer between the water and any lead solder, reducing the risk of leaching.

The water district does this because it is modeled on worst-case scenario conditions, Page said. If older houses likely to have lead-soldered joints show low lead levels, then the chances of elevated lead elsewhere in the water system are low. But if those households show elevated lead levels, the water district needs to determine what caused the spike and what’s needed to lower those levels.

After it detected higher levels of lead in 2010, the Bangor Water District had to elevate its monitoring from once a year to every six months, as well as double the number of households tested from at least 30 to 60.

A solution

What caused the sudden spike in 2010 was a matter of water chemistry. In Maine, surface water sources, such as Floods Pond, tend to have a lower mineral content than groundwater, making them more acidic. As a result, Maine water naturally falls around a six on the pH scale.

(A quick chemistry primer: The pH scale ranges from zero to 14. Between zero and six on the scale is acidic; eight to 14 is basic. A seven is neutral.)

But when naturally acidic water is devoid of minerals, it tends to make the water more corrosive. “The more pure the water, the higher the risk of corrosion,” Page said.

And it’s this corrosion of older fixtures and lead-soldered joints that feeds lead into the tap water. But adding some minerals back into the water neutralizes the acid, raising the pH level. Plus, the addition of minerals builds up a buffer between the water and the plumbing to reduce the risk of corrosion over time.

After the 2010 spike, the Bangor Water District added sodium carbonate to the water to increase the pH to about nine, similar to milk of magnesia. This change caused lead levels to fall over the last five years to the lowest they’ve been in years, Page said.

During the water district’s second round of testing in 2013, lead levels began to drop off, with only four of 60 test sites showing lead levels in excess of the EPA threshold; 90 percent of sites had levels below 11 parts per billion. In the first six months of 2014, the number of test sites in excess of the EPA threshold fell to two of 60, with 90 percent showing levels below 8 parts per billion. This decline was sharp enough for the EPA to take the water district off elevated monitoring.

In the most recent round of testing in 2015, only one of 30 test sites had a lead level above the acceptable threshold; 90 percent of test sites showed levels below 4 parts per billion.

Until all lead is gone from household plumbing, lead monitoring will be an ongoing concern for the Bangor Water District and other public water systems. Page said the water district is monitoring the water chemistry every day in an effort to reduce corrosion and minimize households’ risk of lead exposure.

“We’ve experienced a steady decline in those results but this is a process where every time you go to monitor, there are so many variables,” Page said.