Only a small portion of the earth's water supply is fresh water. With the rate that the human race uses water, how come it never runs out? Fresh water never runs out because it is constantly being renewed by the water cycle. In a water cycle water is always on the move as it changes from a liquid to a gas and back to a liquid.
When water evaporates it leaves behind the materials it contained. The water vapor is not salt water. And when the water falls back to earth it seeps into the ground and becomes groundwater. Groundwater then seeps into spaces within the earth until it is blocked by a rock that is tightly packed and has few spaces. Then the water starts to back up and fill spaces in the soil and rocks above. The top of these water filled spaces are called water tables. If the water table reaches above the surface a pond, lake or stream is formed.
Ponds and lakes are still bodies of water. They get formed when water fills up low lying places. Streams flow downhill and as they flow they join up with other streams and eventually run into the ocean or other large bodies of water.
An underground layer of rock or soil that gets filled with water is called an aquifer. Water can move through an aquifer through very long distances.
Some ground water seeps out of the ground into a spring. Springs occur when the water table meets the surface. They feed water into lakes or streams long after it stops raining.
Most supplies of fresh water for large towns or cities come from reservoirs. They become storage areas for fresh water supplies. Reservoirs are commonly human made, but there are natural made ones too and pipelines are used to transport water from a reservoir.
Fresh water can become polluted in many ways. Aside from the unfortunate dumping of trash into the fresh water, it becomes polluted as the rain or snow picks up pollutants in the air as the precipitation falls to earth. There are chemicals in the air that makes the rain turn into acid. Acid rain harms both living things and property.
Water also gets polluted when there is runoff water. This is water that runs off the land and becomes in contact with the trash on the ground therefore polluting the fresh water supply.
Groundwater is a potential hazard to keeping water fresh. As groundwater soaks down through the sol it can pick up chemicals such as pesticides that contaminate the fresh water. There are also water supplies that get polluted by industries. For example, water that is used to produce paper is slowly filled with fibers and chemicals.
And water is polluted in the household as you flush toilets, wash dishes, brush teeth, or take a bath. Water becomes polluted with waste and is pumped to a plant to recycle. This helps recycle our fresh water supply because it is so small and in great demand. The fresh water cycle is complex and vital to life. Aquifers, reservoirs, and pollution all are key factors in supplying fresh water to earth.
Because only a small portion of the earth's water supply is fresh water, it is important to not only keep it fresh, but also to keep the water cycle running.