All forms of precipitation are caused by the condensation of water vapor in the atmosphere.
All living things require water. It is for this reason that different regions throughout the world exhibit individual patterns of plant and animal growth. In areas where water is plentiful, there are dense forests and lots of animals. In dry regions, there is much less plant and animal life.
How do we get our water? Water travels from the earth to the atmosphere and back again to the earth. This is known as the water cycle. The heat of the sun causes water to evaporate from the surface of oceans, streams, lakes and glaciers. In gaseous form it is carried by air currents into the atmosphere. When the temperature drops, the water vapor condenses and falls to the earth as precipitation.
More than three-fourths of the earth’s surface is covered with water. Most of this water is in the oceans. Ocean water cannot be used for drinking, irrigation, or industrial processes because it is salt water.
Each person drinks about l.5 liters of water a day. People also use water to bathe, cook, and clean. It has been estimated that each person in the United States uses over 400 liters of water daily. Industry also uses billions of liters of water each day. Farmers also use billions of liters of water each day to irrigate farm land. The United States alone uses over 500 billion liters of water each day. Spread this out throughout the world and the use is magnified billions of times over.
The earth’s fresh water and ocean water are also important food sources for the world’s population. Water is a substance most people take for granted. The amount of water we use today will probably double within the next 20 years. Remember a very important point, only about 3 percent of the earth’s water is fresh water and most of this water is locked up in ice. In fact, only about l5 per cent of the earth’s fresh water is available for use by living things, and living things cannot exist without water. Protein, the principal component of cellular material is 70 percent water. Most everything that diffuses into and out of a cell is dissolved in water. Thus, water is called the universal solvent. Because living things constantly need water, and water must be recycled.
Whether we have enough usable water in the future depends on whether we keep pollutants or harmful substances out of the water. Many of our lakes and rivers were important sources of fresh water. But people used them as dumping grounds for wastes and sewage. This has caused them to become polluted. Polluted water is not safe for drinking, swimming, or bathing. Pollution also destroys many of the organisms that live in oceans, rivers, lakes and streams. Some of the pollutants are dissolved materials. Dissolved materials can come from sewage emptied into the water. Some pollutants are suspended particles. These particles can come from factories emptying wastes into the waters. Certain pollutants such as phosphates cause uncontrolled growth of green plants in lakes which may use up the oxygen in the water and cause fish to die. Many pesticides also end up in lakes and streams. As they build up they also cause harm to the water, fish, and other organisms in the water. Water pollution also occurs when heated water from factories is put into streams and lakes. This type of pollution is called thermal pollution. It is usually caused by power plants that use water to cool their generators, then return the water, only now it is warmer than before. Warm water holds less oxygen, thus limiting the number and kind of organisms it can hold.
In this unit I have already discussed two of our more important natural resources, air and water. Along with air and water we have soil and forests. These resources are called renewable resources. They can, but not easily, be replaced after we use them. The air is used over and over again. The water cycle allows us to use water over and over again, although we are able to use less and less because of other factors. Forests are replanted after they are cut down, but not anywhere near the rate at which they are being cut. The soil can be helped along as fertilizers put chemicals back but not as quickly as erosion and depletion are taking their toll on soil. Because we can reuse theses resources, they are called renewable resources.
Some resources cannot be replaced after they are used. These resources are called non-renewable resources. Minerals are examples of non-renewable resources. After a mineral is removed, it is gone. It cannot be replaced by nature. Fuels such as coal, oil and natural gas are non-renewable resources. We are using these non-renewable resources much too quickly. People need these natural resources to survive. These fuels are the main sources of energy for industry, transportation and even our homes. As population increases, the need for these fossil fuels also increases proportionally, so it is imperative that we use them cautiously and conserve.