Researchers wildly underestimated how many people don’t have safe drinking water.

In 2021, the World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF) estimated that 2 billion people worldwide lack access to clean water.

Roughly a quarter of the world’s population might seem bad enough. But on Thursday, a new study published in Science reported that 2 billion was a huge underestimate. New analyses reveal that 4.4 billion people across low- and middle-income countries — over half of the world’s population — don’t have safe household drinking water. It’s not that billions more people lost access to water. Rather, how researchers measure access became much more accurate, and those new measurements showed the problem is much worse than previously thought.

If you’ve always had clean running water at home, it’s easy to forget that drinkable tap water isn’t a given for much of the planet.