Drawing On Science For Kids
OK, the above title isn't as bad as you think. You'll see why as you read on. Water is a part of every living thing (about 90 percent of your body is water) and it covers about 97 percent of the earth's surface as ocean water. Ocean or salt water is a solution of many different salts. The remaining 3 percent is fresh water containing no dissolved salts. Fresh water is found in rivers, streams, lakes, ponds, creeks, glaciers, reservoirs and aquifers (=underground containers that hold water, which has seeped into the ground). Only one-half of 1 percent of fresh water is potable (=safe drinking water). And of this usable fresh water a very small fraction is found on the surface in lakes, ponds, and streams. Most of it is stored in the aquifers. All water found on, under and above the earth makes up what is known as the hydrosphere (hydro=water, sphere= globe).
Less than 3 percent of Earth's water is fresh water. Only 1/3 of this fresh water is available to us as liquid. The remaining 2/3 is frozen in glaciers and ice caps.
In nature water moves in a number of circular paths called the water or hydrologic cycle. This water cycle is powered by the sun's energy. Water on the surface evaporates (=changes from a liquid into a gas) when the sun warms it. This evaporated water comes from oceans, lakes, ponds, streams and land. Plants release water into the air by a process known as transpiration (=release of waste water through small openings in leaves called stomates- see Drawing on Science 9/17/04). Evaporation and transpiration is combined and called evapotranspiration.
Winds carry the water vapor from the oceans over the continentents. In the high atmosphere the water vapor cools and condenses (=changes from a gas into a liquid). This results in cloud formation. When the clouds become full with water, the water is released. Water will then return to the surface as rain or snow. (Aren't you glad that your nose points down? If it pointed up and you got caught in a storm you would have to cover your nostrils to keep the rain out.) Water that falls into rivers and streams is carried back to the oceans as runoff. Water forming puddles on land evaporates back into the atmosphere. Water on the surface that does not evaporate seeps into the ground settling in aquifers. And the cycle continues.
Another path of the cycle involves animals. Animals obtain water by drinking or eating. As a natural process the body accumulates excess water. This excess water must be gotten rid of. Depending on the animal, this is accomplished in two ways: perspiration or sweating and urinating. This getting rid of waste water along with its dissolved substances is the life process,
excretion. Eventually your sweat evaporates and enters the atmosphere as pure water. Urine is flushed down the toilet. The water in sweat and urine eventually evaporates and is recycled. Now I know what you're thinking. No, urine and smelly sweat are not falling on your head when it rains. When water evaporates, any dissolved substances in the water remain behind- only the water vapor rises into the atmosphere. When sweat evaporates, dissolved waste remains behind. Urine flushed down the toilet travels to a waste purification plant where it is treated and purified before being released back into the environment. What results, then, after evaporation and purification is pure water. Distillation is a process involving evaporation. When a mixture of water and dissolved substances is distilled, only the water is collected. The dissolved substances remain behind. Astronauts drink pure, distilled water produced from their own sweat and urine.
To Do: If you'd like a simple experiment on distillation via email, please contact me at the email address below.
Something to Think About: 1. What happens to rain when it falls on the Earth's surface? 2. How much of Earth's fresh water is frozen in glaciers? 3. Where is most of our useable fresh water located? 4. What powers the water cycle? 5. What is evapotranspiration? 6. Droughts and dry spells have been a problem for centuries. How can we conserve water during such times?
In the News: 1. Why was water released from Lake Mead into the Colorado River? 2. What problems have been found in our drinking water?
Questions/comments? E-mail Steve: Drawingonscience @aol.com