The Water Cycle ATOS 7.11

The Water Cycle

By Rusty Perez

Water, like many other things on earth, is an ancient substance made of two elements, hydrogen and oxygen. It is sometimes called H2O because it is two parts hydrogen and one part oxygen. It is found everywhere on earth, even in the driest deserts.

Water in one form or another, covers 71% of our earth. Most of this precious liquid is in our oceans. However, 61% of all fresh water is frozen in glaciers. In developed nations, such as the United States, it is easy to take water for granted. We turn on the faucet and the water is there. But, is water really never-ending?

There is only a finite amount of water on our earth. The water we have is redistributed through the water cycle. Imagine you put a bowl of water outside for your dog. If the dog doesn't drink it all, after a while, that water will disappear through a process called evaporation. Where does it go? On a hot day, the sun heats it up and, little by little, the water turns into microscopic droplets as it transitions from a liquid state to a gaseous state and is absorbed into the atmosphere. The water simply turns into gas and floats away.

But that water hasn't just disappeared. Later, as the temperature of the air cools down, the water also becomes colder. The lower temperature allows the moisture to condense into water droplets. One possibility is that the condensation turns into fog or dew, settling on the leaves of trees or blades of grass. It is also conceivable for it to form a rain cloud and then fall to the earth a thousand miles away.

When the rain falls to earth, it might land in a stream or a lake. It is also feasible for it to land on the earth and sink deep into an underground stream called an aquifer. That stream might later surface into an above ground stream or lake, and a bear might drink it. This cycle of evaporation, precipitation, and return to the water on earth is called the water cycle.

The water we drink daily in many large cities often travels thousands of miles through aqueducts which transport the water from far away and puts it into reservoirs. When the reservoirs are empty, the city runs out of water. But that doesn't mean the earth is out of water, it just means that water hasn't been distributed to the reservoir for that city. Many cities are located in areas where water is scarce. Much of California, for example, is actually a desert, where water is scarce. Technology has allowed humans to transport water from other places to make the Californian desert livable.

So, the next time you turn on a faucet or water a plant with the hose, remember that the water you leave outside might just evaporate. Thanks to the water cycle, the water may return again in the form of dew or fog. But remember that the water that you waste might be difficult to replace in your city.