A new study suggests that the stuff used to disinfect tap water, chlorine vs. monochloramine, might be linked to how often people get Legionnaires’ disease. And honestly? The difference is kind of surprising.

Clean water is a basic expectation in the United States, yet millions of Americans still live in areas with unsafe or unreliable drinking water. High-profile crises like Flint’s lead disaster grabbed national attention, but many other cities continue to struggle with contamination that stems from aging infrastructure, poor regulation, political conflict, or environmental injustice.