150 million people in the United States have some of their drinking water filtered by forests. Forests, especially old, undisturbed ones, not only contribute to replenishing our groundwater but also act as the first source of filtration for streams, ponds, and reservoirs. Approximately 74 percent of all water in the U.S. is sourced from above-ground water sources. Prioritizing the protection of old-growth forests is an easy way to ensure that we continue to supply Americans with clean drinking water.
How do forests produce clean water?
The ability of forests to produce clean water originates from their involvement in the water cycle. Forests are major sources of evapotranspiration, a process where water moves from the earth to the atmosphere through the evaporation of water from the soil and transpiration of water from the leaves and stems of plants.
Through evapotranspiration, forests directly contribute to local and distant rainfall for the regions they inhabit. On average, at least 40 percent of rainfall over land originates from evapotranspiration, indicating that forests and plants are a key contributor in regulating rainwater. When forests are destroyed by human processes, such as logging, or natural events, such as wildfires, that source of rainwater is lost for the surrounding areas, which can significantly impact the replenishment of freshwater sources.
Forests also contribute to increased infiltration, the part of the water cycle that returns water to below-ground sources. High-elevation forests have been shown to have higher rates of infiltration than lands cleared for agricultural uses. Forests with more extensive root systems have also been shown to enhance the flow of rainwater to surface depths that areas with less complex root systems would be unable to reach, thus enhancing the replenishment of deep groundwater sources. This is especially important as we consider the benefit of old-growth forests concerning clean water supplies.
Why are old-growth forests particularly important when it comes to clean water production?
By definition, old-growth forests are inhabited by older (typically 80+ years) trees with intricate root systems that have been undisturbed for decades. These root systems enhance the infiltration capabilities of old-growth forests and increase their capacity for filtering rainwater into clean, ready-to-source groundwater. The older a forest is, the longer its soil can accumulate organic matter from the life and death of various plants, animals, and other forest-dwelling organisms. This accumulation of matter, and the roots of trees and plants that dwell within it, create the perfect environment for reducing pollutant and excessive nutrient levels of the water passing through it.
Older forests also mitigate floods. Compared to land areas that have disturbed soil and fewer trees, such as agricultural lands, older forests are far more successful in reducing stormwater runoff. Reducing stormwater runoff reduces the likelihood of contaminants like agricultural runoff, household chemicals, and other pollutants reaching surface water supplies, where they would have to be filtered out by municipal water treatment systems. Decreasing the need for filtering water through man-made systems also reduces the costs associated with producing and consuming clean water, which is another reason it is so important to protect old-growth forests. The forests that are our most successful filters for the water we use to drink, cook, and clean are always going to be our oldest ones. Leaving older forests undisturbed protects not only their majestic ecosystems but also their potential as a cost-effective solution for producing clean water, which will only get more expensive as the effects of a warming planet make freshwater sources more scarce.
Why is prioritizing forests as clean water sources important for the environment and our economy?
In the simplest of terms, forests improve raw water quality, which is associated with reduced drinking water costs by reducing capital costs for water treatment plants. Successful watershed restoration projects have led to reduced spending on water treatment facilities, as is the case in New York City. In 1997, the Watershed Memorandum of Agreement was signed by numerous stakeholders, establishing a watershed protection program that set forth to preserve the drinking water supply for New York City residents and also to ensure the continued economic growth of upstate watershed communities. This restoration and preservation project is estimated to have saved New York City at least $6 billion by negating the need to construct a new water treatment plant and saved an additional $300 million in operational costs each year since.
As our climates change in response to a warming planet, already dwindling freshwater resources will become even more tenuous. In the face of this threat, we must prioritize forest conservation, especially old-growth forest conservation, to mitigate the potential harm to human populations and local ecosystems. The U.S. Forest Service found that the Eastern, Southern, and Pacific Southwest regions have the most watersheds that are of the highest importance to providing surface drinking water to human populations.
The dark blue areas in the map above, which are important for drinking water, are also home to some of our country’s oldest forests.
Old-growth and mature forests that have been inventoried by the U.S. Forest Service are in the map below.
The eastern half of the United States lacks old-growth forests because of the intense logging that occurred from the 19th into the 20th century in that region. Approximately two-thirds of the undisturbed forests in the Eastern U.S. were completely deforested due to logging from 1850 to 1920. Unfortunately, these crucial ecosystems continue to face significant threats, despite their ability to provide clean water to millions of people.
Our oldest forests are threatened
All across the country, our oldest forests managed by U.S. Forest Service and Bureau of Land Management are at risk of being logged by timber companies.
Aside from disturbing large swaths of soil and building impervious roads, which contribute to increased runoff, many logging projects also create large areas of clear-cuts. Clear-cuts slice through forests like large, open wounds, reducing their capacity for evapotranspiration and hindering their ability to distribute water back into the groundwater system.
Trees have been the foundation of human civilization for millennia, since the days when nomadic cultures were the primary inhabitants of Earth’s vast continents. They have long provided a source of shelter, food, and safe drinking water. Cutting down trees not only harms the complex ecosystems they support, but it creates more work for downstream communities when treating their water. This cost can be avoided by supporting the stewardship of forests and protecting the watersheds they supply. We must all do our part to protect the lands that provide us with our most precious resource. Use your voice today to support the protection of old-growth and mature forests so we can continue to secure clean water access for our communities for generations to come.
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Ellen runs campaigns to protect America’s beautiful places, from local beachfronts to remote mountain peaks. She sits on the Steering Committee of the Arctic Defense Campaign and co-coordinates the Climate Forests Campaign. Ellen previously worked as the organizing director for Environment America’s Climate Defenders campaign and managed grassroots campaign offices across the country. Ellen lives in Denver, where she likes to hike in Colorado’s mountains.
