Everything from tree roots to leaves play a role in keeping our water in lakes, rivers, and aquifers clean. This is important because 75 percent of Minnesotans get their drinking water from the forested parts of the state.
Forests act like an umbrella, filter, and sponge to keep water clean.
Trees and understory plants slow down and guide rain as it falls to the ground. This umbrella effect prevents soil from washing away into lakes and streams. Plus, it lets water seep deep to replenish groundwater in aquifers.
The large and numerous pore spaces in forest soils trap sediment, nutrients, and pollutants suspended in rainwater. This filter effect prevents contaminants from entering ground and surface waters.
The pore spaces that filter contaminants also soak up and store rainwater and snowmelt like a big sponge. Over time, the forest soil slowly releases water and helps keep soil in place, reducing flooding and erosion.
Forest and Clean Water Facts
- Retaining and managing forests is one of the best ways to protect drinking water and reduce the cost of water treatment.
- A 10 percent increase in forests in a watershed results in a 20 percent decrease in treatment and chemical costs downstream.¹
- Forests produce four times less storm runoff than an agricultural field during a 4-inch rainfall.²
- About three-quarters of Minnesotans get their drinking water from the forested parts of the state.
- Sound management of forested public lands surrounding the Mississippi River ensures clean drinking water for more than 1 million Minnesotans.
- Urban trees decrease water entering storm sewers by capturing rain, increasing flow of water into the soil, and transpiring water into the air.
- Larger trees intercept more water: a typical 20-year-old hackberry in Minneapolis intercepts 1,394 gallons of rainfall per year while a typical 40-year-old hackberry intercepts 5,387 gallons.³
1. Ernst, Caryn. (2004). Protecting the source. Land conservation and the future of America's drinking water. The Trust for Public Lands and the American Water Works Association.
2. Purdue Extension Safe Water Office. Land use and water quality. Accessed 2/23/2015.
3. McPherson, E. Gregory; Simpson, James R.; Peper, Paula J.; Maco, Scott E.; Gardner, Shelley L.; Cozad, Shauna K.; Xiao, Qingfu. )2006). Midwest community tree guide: benefits, costs, and strategic planting. Gen. Tech. Rep. PSW-GTR-199. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 99 p