Forested lands across the U.S. provide 83 million people with at least half of their water, according to a broad new study of surface water sources for more than 5,000 public water systems. 125 million people, or about 38% of the country's population, receive at least 10% of their water from forests. In the arid western U.S., 39.5 million people get more than half of their surface drinking water from forests that are increasingly under threat of wildfires.