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WSU/Pend Oreille Extension introduced the Sense of Place series in 1999, with a focus on local landscape and natural history of Pend Oreille County, Washington. A partnership with the Kalispel Tribe of Indians Natural Resources Department has allowed us to expand this program through EPA funding to include more classes, a newsletter and this website.

Conservation and the Water Cycle

Water is probably the natural resource we all know best. All of us have had firsthand experience with it in its many forms - rain, hail, snow, ice, steam, fog, dew. Yet, in spite of our daily use of it, water is probably the natural resource we least understand. How does water get into the clouds, and what happens to it when it reaches the earth? Why is there sometimes too much and other times too little? And, most important, is there enough for all the plants, and all the animals, and all the people?

Water covers nearly three fourths of the earth; most is sea water. But sea water contains minerals and other substances, including those that make it salty, that are harmful to most land plants and animals. Still it is from the vast salty reservoirs, the seas and oceans, that most of our precipitation comes - no longer salty or mineral laden. Water moves from clouds to land and back to the ocean in a never ending cycle. This is the water cycle, or the hydrologic cycle. Ocean water evaporates into the atmosphere, leaving impurities behind, and moves across the earth as water vapor. Water in lakes, ponds, rivers, and streams also evaporates and joins the moisture in the atmosphere. Soil, plants, people, and animals, and even factories, automobiles, tractors, and planes, contribute moisture. A small part of this moisture, or water vapor, is visible to us as fog, mist, or clouds. Water vapor condenses and falls to earth as rain, snow, sleet, or hail, depending on region, climate, season, and topography.

Every year about 80,000 cubic miles of water evaporates from oceans and about 15,000 cubic miles from land sources. Since the amounts of water evaporated and precipitated are almost the same, about 95,000 cubic miles of water are moving between earth and sky at all times.

Storms at sea return to the oceans much of the water evaporated from the oceans, so land areas get only about 24,000 cubic miles of water as precipitation. Precipitation on the land averages 26 inches a year, but it is not evenly distributed. Some places get less than 1 inch and others more than 400 inches. The United States gets about 30 inches a year, or about 4,300 billion gallons a day. Total streamflow from surface and underground sources is about 8.5 inches a year, or about 1,200 billion gallons a day. This is the amount available for human useÑhomes, industry, irrigation, recreation. The difference between precipitation and streamflow is 21.5 inches a year, or 3,100 billion gallons a day is the amount returned to the atmosphere as vapor. It is roughly 70 percent of the total water supply. It includes the water used by plants.

People can exist on a gallon or so of water a day for drinking, cooking, and washing though we seldom do or have to. In medieval times people probably used no more than 3 to 5 gallons a day. In the 18th century, especially in Western nations, people were using about 95 gallons a day. At present in the United States, people use about 1,500 gallons a day for their needs and comforts including recreation, cooling, food production, and industrial supply.

It is our management of the precipitation available to us that determines whether or not we have both the quantity and the quality of water to meet our needs. It is our obligation to return water to streams, lakes, and oceans as clean as possible and with the least waste.

Adapted from Natural Resources Conservation Service publication http://www.wcc.nrcs.usda.gov/factpub/aib326.html

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