Without soil to hold water and to share it with plants through the growing season, the families of life on which we depend would not exist. The value of a stream or pond extends beyond its banks across the valley that collects skywater, stores it for plant and animal use, and allows the excess to seep into a channel and be carried away for the benefit of life in streams, ponds, estuaries, bays, gulfs, and the ocean. Some of the water falling on a watershed sinks down and is stored as groundwater in underground reservoirs known as aquifers. A great deal of skywater evaporates, especially if it collects on the surface faster than the soil can absorb it. Evaporation carries water into the atmosphere as vapor, an invisible gas, where it is recycled, eventually condensing on wind-borne particles such as dust and spores, and falling as precipitation again, and again, and again.
Evaporation is a purifying process that prevents pollutants from rising into the air.
Evaporation assures the long-term stability of climate itself, and the survival of all forms of life. In the green, heavily forested State of Maine, much of the water that falls on a watershed flows through the stems of trees and other plants into their leaves. Transpiration lowers pressure in a plant's leaves so that a flow of moisture from the roots is drawn upward to replace what is lost to the air. Skywater that falls on a watershed and is not stored as groundwater, doesn't evaporate, and isn't returned to the air by transpiration, this water flows through the soil according to the pull of gravity and the lay of the land, to seep into the banks of a stream, pond, or wetland lower down in the watershed. A watershed receives, stores, recycles, and delivers water to the roots of plants through the growing season, and feeds water into streams, ponds, estuaries, and ultimately the ocean.