Forests: Nature’s Water Purifier

The Nature Conservancy is Helping to Keep Your Drinking Water Healthy.

The Forest- Freshwater Connection

Explore the connection between healthy forest and our drinking water.


Story Highlights
  • The Nature Conservancy is protecting forests, which absorb nutrients that can spoil water quality.

By Randy Edwards

Next time you walk through a forest, imagine that the trees are affixed to the end of your kitchen faucet like a large green purifier, cleaning the water before it splashes, crystal-clear and cool, into your drinking glass.

It’s hard to think of it that way; a natural forest is a messy thing, a chaotic jumble of plants and animals blanketed by leaf litter or pine needles. But the civil engineers who are responsible for safe drinking water have known for years that source water flowing from forested watersheds is easier and cheaper to treat than the water that runs off city streets or agricultural fields.

That’s because forest root systems absorb nutrients that can spoil water quality, and bind soil together to prevent erosion from polluting streams. Mature trees along a river provide shade to moderate water temperature. Protecting forested floodplains reduces flooding, which in turn decreases sediment and polluted runoff.

So, if you want a drink of clear, cool water, look downstream from a healthy forest.

Pennsylvania Forests

But those healthy forests are threatened throughout Pennsylvania, by unsustainable forestry and agricultural practices and by urban development. And as forests are destroyed, water quality suffers. That’s one important reason why The Nature Conservancy is protecting forests along streams from the Pocono Mountains – where forests protect Upper Delaware River tributaries and source water that eventually flows to Philadelphia – to northwest Pennsylvania’s French Creek, upstream from Pittsburgh.
Water treatment experts in Pittsburgh know the connection between the forests we preserve and the water we drink.  About 90 percent of the city’s drinking water supply comes from the Allegheny River, and water treatment experts in Pittsburgh say they’ve always known that raw water from forested watersheds is easier to treat. In recent years, regulators have urged municipalities to pay as much attention to the water coming into their treatment plants as they do to the water leaving the plant for distribution.

Pennsylvania’s French Creek is one of the tributaries to the Allegheny upstream from Pittsburgh, and it provides a source of abundant, relatively clean water – largely because the watershed is heavily forested. The Conservancy, in a partnership with the Western Pennsylvania Conservancy and the French Creek Valley Conservancy, is working to keep it that way.

A Conservation Twofer

We didn’t come to French Creek to protect drinking water but because we recognized, nearly 20 years ago, the extraordinary biological diversity of this watershed. Along its 117 miles, from western New York across northwestern Pennsylvania, the river is home to more than 28 freshwater mussel species, including 13 that are listed as endangered in Pennsylvania and the federally endangered northern riffleshell and clubshell.

But that’s the beauty of protecting forested watersheds. Conserve a floodplain forest and you’ve not only protected drinking water for communities downstream, but you’ve also preserved habitat for birds, fish, and other animals that rely on clean streams and healthy forests. 

French Creek is just one of numerous places throughout the country where we’re restoring floodplain forests, supporting improved forestry practices, and contributing new knowledge to our understanding of how forests protect freshwater.

So next time you turn on your tap, picture a stream passing through a deep, cool forest – nature’s water purifier.