The Hydrologic Cycle

Freshwater is necessary for humans to live, and a cornerstone of modern civilization. It also happens to be an excellent solvent, capable of absorbing a number of solids. Humans do an excellent job of leaving solids in the path of flowing freshwater, many of which have a detrimental effect on our health. This problem multiplies as human population continues to grow at a rapid, though slowly decreasing, rate. The following is a cursory look at the interaction of these solids, a.k.a. pollutants, throughout the hydrologic cycle. Click here to view a graphic of the hydrologic cycle.

Starting in the salty oceans, heat is input into the system from the sun, which causes water to evaporate. The salt is left behind, giving the air vaporized freshwater. As the moisture laden air rises, it cools and forms clouds. This initial phase is the first place water can encounter pollutants. Industry and combustion engines emit pollutants into the atmosphere. These pollutants can be dissolved in the water, giving rise to acid rain. This can be detrimental to aquatic ecosystems when the water vapor condenses and falls back to the earth.

When the clouds precipitate, they introduce the water to its next round of pollution exposure. On the ground, water encounters pollutants from every aspect of human society. Vehicle drippings, tire rubber, fertilizers, pesticides, herbicides, pharmaceuticals, cleaning fluids and disturbed earth. This polluted water can also percolate into the soil and the groundwater system. Where ever it goes, it is costly to remove. Ultimately, this run-off returns to the ocean, carrying with it the toxic soup of chemicals it picked up along its way. Let us not forget sewage, which returns to the river untreated in some parts of the world.

Humans have water treatment facilities to deal with some of these pollutants. Some are not removed, as the cost is to prohibitive. There are also natural means of purifying water. Some microbes do eat these chemicals, but the most important cleaning agent in nature is the wetland. Wetlands are essentially the Earth's kidneys. They filter out impurities, and lock them up in plant material. The water is purified by the plants, and as it percolates beneath the surface.

Freshwater is essential for humans. We all need to make the preservation of good water quality a priority in our daily lives. Do not dump vehicle fluids and chemicals into the trash or the ground. Dispose of them properly. Do not over fertilize your lawn. It may not seem like much fertilizer, but when this small amount is multiplied by hundreds of millions of people, the amount of excess fertilizer would be huge. Finally, support efforts to restore and protect wetlands. They were once targeted as swamps, but we now know they help us a lot more than we thought. If everyone does his or her part, we can have a sustainable supply of good quality freshwater for generations to come.

For more information on water quality legislation in the U.S. click here.

Learn more about source water protection by clicking here.