Access to high-quality water will be a defining feature of the 21^st century. Record heat waves and drought are not only leading to more frequent and intense wildfires but are also putting one of life’s most valuable resources at risk: the water we drink.

A new Forest Service research report describes how extensively public drinking water systems rely on national forests and grasslands.

Water use per person has been declining for decades; however, a variety of factors such as population growth, food production and ecosystem conditions under a changing climate are contributing to overall greater demand for water – especially in certain parts of the country.

In the West, national forests and grasslands supply drinking water to almost 90% of the people served by public water systems. Some western cities, like Aspen, Colorado, and Portland, Oregon, are more than 90% dependent on national forests alone for their drinking water. The story is similar in the eastern U.S., though most of this water is supplied by private forests.

Still, more than a century of research has demonstrated that forested lands provide the cleanest and most stable water supply compared to other lands. Within the lower 48 states, more than 99% of people who rely on public drinking water receive some from forested lands.

This report is the first of its kind to measure how individual national forests and grasslands contribute to surface drinking water supplies while accounting for networks of pipelines and canals that divert water from the source to areas of high need, also known as “inter-basin water transfers.”