Sometimes it seems like California—the concept of California, rather than just the location—has a sense of entitlement when it comes to water. It’s not just rights or ownership of the stuff, but also the drama that follows water wherever it flows. Hardly a month after Flint, Michigan made national headlines due to lead contamination, the city of Stockton1, in California’s agricultural Central Valley, is the center of its own growing water controversy.

This Monday, just a few days after discussing Flint on the Late Show with Stephen Colbert, environmental activist Erin Brockovich appeared at a Stockton town hall meeting. The topic was a family of disinfectant chemicals called chloramines that the city has recently started adding to its water supply. Speaking to a room of 1,200 concerned citizens, Brockovich warned the city's leaders they were "on the fast track to creating the next Flint."

The US has been using chloramines to purify water since 1929. Most of that time, the chemicals were noncontroversial. In the early 2000s, however, Washington DC switched from chlorine to chloramines, which corroded the city's aging lead and copper pipes. A congressional investigation found negligence and obfuscation at every level, from the regional water authorities to the Environmental Protection Agency and Centers for Disease Control and Prevention.

Washington's case stoked fears on a national level; this isn’t just about lead poisoning. Chloramines have a small cancer risk, and a small number of people report things like rashes, breathing problems, and digestive issues after using chloramine-treated water.

On the other hand, DC's crisis is the only real flashpoint in 90 years of chloramine use. And Stockton is only rolling out its chloramine treatment to homes in the northwest part of the city, which is newer and has pipes made from PVC and copper. No lead, no cancer clusters, nothing beyond the anecdotal evidence of those acute dermatological, respiratory, and digestive issues. No smoking gun.

That calms the fears of Stockton’s residents exactly as much as you’d expect. Stockton is a river city, sitting on the eastern banks of the Sacramento-San Joaquin River Delta. Through a twist in California's water law, the city only recently got rights to actually use that water. Before 2012, it drew most of its water from reservoirs in the nearby Sierra Nevada mountains. "The problem, of course, is that there are lots of issues with Delta water. It's just not as good as reservoir water," says Alex Breitler, a reporter for the Stockton Record who has covered the city's chloramine saga for years.

And that saga began with chlorine—the disinfectant Stockton had been using without incident until the city switched to Delta water—and plants.

When plant matter like leaves, bark, and wood decay on the forest floor, some of the microscopic organic particles leech into the water system. These aren't dangerous on their own, but when the organic molecules encounter chlorine, they turn into what are known as disinfectant byproducts, which can cause cancer in humans. "Drinking water standards are based on drinking two to three liters a day for 70 years," Robert Brownwood, field supervisor for CalEPA's State Water Resources Control Board. "And whether drinking that much raises your risk of developing cancer in your lifetime by more than one in a million."

After Stockton switched to Delta water, which has a lot more organic matter than Sierra snowmelt, the city twice violated the EPA's rules on disinfection byproducts.

This has to do with chlorine's chemistry. After it leaves a treatment plant, water can stay in service pipes for more than a week before people use it to water their lawns, make Kool-Aid, or hose off their BMWs. Water authorities add chlorine to kill any dangerous pathogens that could sneak into the pipes along the way. This is why you probably don't know anybody who has died recently from cholera, typhoid, giardia, or any number of other 19th century mass killers. "In the year 1913, an estimated 17 people in every 100,000 were dying from drinking the water," says Brownwood.

But chlorine has a really short half life, so water engineers use a lot of it to make sure it doesn't all break down before the treated water reaches its source. If that water has a lot of natural organic molecules—like the stuff sucked from the Delta—all those chlorine particles can react and form carcinogenic disinfectant byproducts. That’s how Stockton got into trouble with the EPA.

Chloramines are basically chlorine spiked with ammonia, and they were supposed to be Stockton's fix. Chloramines can also interact with organics to create carcinogens, but to a much lesser degree. For one, the ammonia part makes the chloramine molecules last longer. Water engineers don't have to use as much of the stuff, which leads to fewer organic interactions. "The other advantage is chloramines are a weaker oxidant, and do not react with organics strongly," says Haizhou Liu, an environmental engineer at UC Riverside. Less chemicals equals less cancer. Everyone should be happy, right?

Wrong. When the city announced the switch in 2014, the response was immediate and negative. People calling in to complain of skin rashes, breathing problems, and other allergic-seeming reactions. “We had a number of folks calling about skin rashes and other things,” said Mel Lytle, head of Stockton's municipal utilities department, quoted in a recent article by Breitler in the Stockton Record.

Here’s the funny part: The city hadn’t actually started the chloramine treatment yet. It didn’t until January 13 this year.

Don't roll your eyes. "There are some who say these people are imagining these kinds of effects," says Bruce Macler, toxicologist for the EPA's California, Arizona, and Nevada regional office. "I don’t say that, and I don’t believe that they are." However, he says with few exceptions, the medical community has not vetted the hundreds of anecdotal complaints. Before the EPA can take action, the CDC would have to recognize a risk, and so far the agency has not.

Macler sits on the chloramine regulatory review board, and he says plenty of researchers are looking into chloramine risk. "I have just been reviewing chloramines, and the data that has come out has continued to support these chemicals are safe," he says.

None of that satisfies activists like Denise Johnson-Kula, resident of Menlo Park, CA, and president of Citizens Concerned About Chloramines. While taking a shower in 2004, Johnson-Kula had a severe coughing fit that sent her to the emergency room. And it kept happening. Things got so bad that she drank only bottled water, and would only shower on the weekends, at friends' houses. "Our spring water costs and showering out of town cost us $7,000 in one year," Johnson-Kula says. But well before the year mark she heard tell that the San Francisco Public Utilities Commission had recently started using chloramines.

She called to inquire, and found out that the district had started adding the chemicals the day before her initial attack in the shower. "I'll never forget how I got a very rude response, the man said, 'You couldn't have been experiencing symptoms because you live a day away from the water plant,'" says Johnson-Kula. Her water, he told her, would have taken much longer to travel from the treatment plant to her house. Peeved and undeterred, she started CCAC to raise awareness and fight back against the San Francisco Public Utilities Commission.

Johnson-Kula says over 2,000 other people have written her reporting things like rashes, respiratory inflammation, and irritable bowel syndrome. Although she admits the figure isn't vetted by outside research, she estimates around 30 percent of people experience side effects like these within a month of their cities switching to chloramines. "But not everybody reports it, because people have different sensitivity levels," Johnson-Kula says. She believes her own sensitivity is the result of a lab accident she was in while a biochemistry student at UCLA.

Again, hold off on the eye rolls. EPA toxicologist Macler says this kind of sensitivity isn't out of the question. Have you ever eaten something, gotten sick, and wound up with a lifelong aversion? "That's not in your head. You’re really smelling the food, and that smell is really triggering the aversion. I can't eat meatloaf, and it's really sad." He says the same kind of things happen to people who have been exposed to harmful chemicals. If you get exposed to a toxic, raw form of chloramine, and it gets into your lungs, you'll have scarring forever and will be sensitive to future exposure, Macler says. But chloramines in drinking water are so diluted he thinks it's very unlikely they could trigger such reactions. Besides, not everyone who complains has a history of exposure. "These cases are all very frustrating, because their symptoms are all over the place." Not the kind of uniformity you'd need to conduct a real epidemiological study.

Beyond the fear and the science, Stockton's city council has to make a decision—a tough one. If the city stays the course and keeps the chloramines in the system, it will do so against a groundswell of public opinion. If it goes back to chlorine, the city council will once again be in the position to violate federal disinfectant byproduct rules—not to mention expose its citizens to known cancer risks. The politically astute but practically expensive choice would be to go back to chlorine but also install expensive things like UV lights or carbon filters to remove organic material from the water so the chlorine can't do its dirty work.

In the end, politics could trump science. As Oscar-winner Julia Roberts once said (in the movie Erin Brockovich), "Look, I don't know shit about shit, but I know right from wrong!" That’s probably relevant here, right?

1 No relation exists between the city of Stockton and this author.