The Environmental Protection Agency (EPA) is funding four new research projects into a fundamental drinking-water challenge: how to make sure water stays clean of illness-causing microbes without accidentally creating toxic chemicals.

The chemicals are called disinfection byproducts, and have been a known problem for years. Some 295 million people drink water where one type of byproduct has been detected at levels above the Environmental Working Group's suggested health guidelines, according to the advocacy group's drinking water database.

Part of the problem comes from a delicate balance in the water system. Many utilities add extra disinfectant at their treatment plants so that the water stays clean as it travels through water towers, water mains, service lines and, ultimately, to peoples' homes.

Add too little of the common disinfectants chlorine, chloramines or ozone, and pathogens like the bacteria Legionella can sneak into the system, researchers said. Add too much of these, and potentially dangerous disinfection byproducts can form.

A few of the byproducts already have drinking water limits enforced by the EPA. But many exist that are not regulated, and scientists are now racing to figure out exactly how big a problem they are — and how we can stop them from coming out of people's taps.

"Hopefully, we can make recommendations for what U.S. water utilities [should use to disinfect], depending maybe on the region they're in, the types of water sources that they are using," said Raymond Hozalski, an environmental engineer at the University of Minnesota.

His research team and three others received a combined $8.5 million this summer from the EPA to study what the right disinfection mix will look like.

It's not entirely clear why the chemicals created by disinfection are gaining new attention from the EPA now. The agency did not respond to a request for comment.

"It's really good to see this kind of movement forward on this issue," said Sydney Evans, a senior science analyst with the nonprofit Environmental Working Group. But, she added, "This has been an issue for a long time."

Potential problems with disinfection byproducts have been eclipsed in recent years by concerns over the toxic human-made chemicals known as PFAS, or per- and polyfluoroalkyl substances, said Patrick Shea, general manager of St. Paul Regional Water Services. The EPA finally proposed drinking water limits for some PFAS this year.

And over time, better technology has allowed scientists to detect more disinfection byproducts than in the past, said Mary Jo Kirisits, an environmental engineer at the University of Texas at Austin, who is leading one research team that spans several institutions.

"We've got to be looking ahead at: What are some of the unregulated byproducts?" she said. "Is it possible that some of those have health effects that we should be concerned about?"

Chasing a bug

Water systems use disinfection to control microbes that make people sick. But some of these tiny organisms are hard to stop entirely — a problem researchers will have to address as they figure out the best ways to clean drinking water.

The four teams will focus on "opportunistic" pathogens, so-called because they tend to infect older people or the immunocompromised. The pathogens each group is looking at also vary, but the four teams will all look for a leading cause of waterborne illness in the United States today: Legionella.

The bacteria and the condition it causes, a lung infection called Legionnaires' disease, are named for the 1976 American Legion conference in Philadelphia where an outbreak led scientists to identify the bug. Legionnaires' sends between 93% and 96% of people with confirmed cases to the hospital, and 6% to 7% of those infected die, according to Centers for Disease Control and Prevention's (CDC) most recent surveillance report.

Legionella has to be inhaled from water droplets to cause an infection. That means that showers and hot tubs can be points of potential exposure.

It's also been on the rise in the United States for the last 20 years, according to the CDC. Public health authorities haven't changed their surveillance methods for Legionnaires' during that period, Hozalski and the other researchers agreed, indicating that we're not getting better at catching the cases — some other factor is causing people to fall ill more often.

While outbreaks are relatively rare, health officials in Minnesota have noticed an increase.

"Historically, there would be maybe one outbreak every few years. And then, in the past few years, it's been about one per year," said Karla Peterson, supervisor for the community public water supply unit at the Minnesota Department of Health.

Jade Mitchell, an environmental engineer at Michigan State University and a study leader, said an aging U.S. population may mean there are simply more people who can be affected by Legionella. It may also be a problem in communities that have lost residents, leaving behind oversized pipes where water sits for longer, because fewer people are using it.

"We know that water age affects Legionella concentrations," Mitchell said, because as water sits in a pipe, the extra disinfectants that utilities put in will wane, giving Legionella an opportunity to flourish.

Getting the mix just right

Just like some conditions make it more likely for bacteria to spring up, others make it more likely that disinfectants will create new, harmful chemicals in the water system.

Take a cup of water out of the Mississippi River, a drinking water source for many communities, and you'll see a reddish tinge, said Shea, the water system manager in St. Paul. That's a sign of organic matter, or the dissolved remains of leaves and other plants that end up in the river.

But adding disinfectants to water rich in organic matter is a recipe to create potentially harmful byproducts.

Both Minneapolis and St. Paul use the Mississippi as a water source. If the utilities for the Twin Cities added only chlorine to that water, they would risk breaking EPA limits on the small group of byproducts that are already regulated, Hozalski said.

Instead, they use a chemical called chloramine — but that doesn't mean there aren't any byproducts left over. Adding chloramine to the river water can instead create the chemical NDMA, (short for N-Nitrosodimethylamine) an unregulated byproduct which has been linked with liver problems and some cancers after studies in animals.

NDMA is also found in many other places, like in beer and some cured meats.

But water systems like St. Paul are still working on ways to cut down on the chemical, even if it's not yet required by EPA. It can often take the agency decades to begin regulating dangerous substances, such as PFAS.

Shea said the system tested a new disinfection method with Hozalski that will use ozone in addition to other chemicals — a key feature that will be installed with ongoing upgrades to the system's water treatment plant in Maplewood.

The utility had already added new filters to remove some of the organic matter that can later be an ingredient for dangerous byproducts. It also stopped using a nitrogen-based additive in the treatment process that had the potential to turn into NDMA, Shea said.

The addition of ozone will "give us more tools to kind of attack those organic materials before we add chlorine," Shea said.

This is the kind of complex chemistry and fine-tuning that the four research teams may end up recommending to other utilities. But the fixes will depend heavily on the region and the source of their water.

Ultimately, Evans said she hoped that the continuing science would encourage better water regulations across the board — so the water that enters a treatment plant is cleaner to begin with.

"If we can get regulations in place to [better] protect source waters … it won't even be a consideration. The water quality will be better," she said.

This story is a product of the Mississippi River Basin Ag & Water Desk, an independent reporting network based at the University of Missouri in partnership with Report for America, funded by the Walton Family Foundation. Sign up to republish stories like this one for free.