The World Health Organization notes that only about 73% of the world’s population have access to drinking water that is both nearby and free from contamination, leaving billions of people who aren’t afforded such a basic luxury. Even worse, at least 1.7 billion people have to drink from a water source that’s contaminated by human waste.

And while there are notable exceptions such as the Flint water crisis, those of us living in the United States have few reasons to worry about such the safety of our drinking water. “In relationship to the risk of illness associated with other countries around the world, our drinking water ranks fairly highly as we use advanced testing measures to ensure that drinking water is safe and free from both chemical and microbial contaminants,” says Rachel Noble, a distinguished professor of marine sciences at the University of North Carolina at Chapel Hill.