New research reveals how critical forests are to drinking water supply

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.   

Quantifying the Role of National Forest System and Other Forested Lands in Providing Surface Drinking Water Supply for the Conterminous United States (GTR-WO-100), a new Forest Service research report, describes how extensively public drinking water systems rely on national forests and grasslands.

Access to high-quality water will be a defining feature of the 21st century. Water use per person has been declining for decades; however, a variety of factors are contributing to overall greater water demand, including population growth, increased demand for irrigated food crops, and impacts from drought and climate change. At the same time, warming will result in a reduction of water available to all ecosystems, including forested ecosystems. Maintaining the health and extent of current forests will be key to providing consistent water supplies into the future.   

I’d like to highlight a few key messages from the report that demonstrate how critical national forests are to our drinking water supply in the lower 48 states. In the West, national forests and grasslands supply drinking water to almost 90% of the people served by public water systems. Similarly, national forests and grasslands in the west comprise 19.2% of the total land area but contribute 46.3% of the surface water supply. Some western cities, like Aspen, Colorado, and Portland, Oregon, are over 90% dependent on national forests alone for their drinking water.

In the East, drinking water is still provided by forested lands, though these are mostly privately owned forests. Over a century of research has demonstrated that forested lands provide the cleanest and most stable water supply compared to other land types. Within the lower 48 states, over 99% of people who rely on public drinking water systems receive some of their drinking water from forested lands. 

This is the first report to assess the contribution of individual national forests and grasslands to surface drinking water supplies while also accounting for inter-basin water transfers—networks of pipelines and canals that divert water from its source to high-need areas. Inter-basin transfers can be an important source of drinking water, particularly for western cities. The Los Angeles area, which serves 7.1 million people, receives over 68% of its water supply from forested lands in California and Colorado.

By showing where our drinking water comes from at a fine scale, this report supports implementation of USDA’s Wildfire Crisis Strategy, the Bipartisan Infrastructure Investment and Jobs Act, and the Inflation Reduction Act. The actionable information provided in this report will help land managers to prioritize forests and watersheds for hazardous fuels reduction, watershed management and restoration treatments.

I’m excited to see how this  data helps land managers and policy makers in their efforts to protect communities from wildfire while maintaining clean and reliable drinking water.