What kinds of water are there?
We are really talking about two sources of water when we talk about water supply. They are groundwater and surface water. We were lucky enough to visit three water companies that showed us how water supply works from both of these sources.
What is surface water?
Surface water is the easiest water to understand because we see it every day. It is any water that travels or is stored on top of the ground. This would be the water that is in rivers, lakes, streams, reservoirs, even the oceans--even though we can't drink salt water. Snow can become surface and groundwater. An example of this is when it snows a few times on a mountain. The snow might not melt in between snows. When it warms up in the spring, there could be too much water for the earth to absorb. This causes the melted snow water to run down the mountains as surface water until it reaches a body of water. Sometimes surface water sinks into the ground and becomes ground water. We visited a few water facilities and each one mentioned runoff. Runoff is the water that runs in gutters, off roofs, and out of mall parking lots when it rains. This is surface water, too. Runoff is a problem because it carries bad things like car oil, road salt, and trash into the water supply. Surface water is treated before it becomes drinking water. This is done because things like leaves, fish, animal droppings, and boat fuel can easily get into lakes, streams, and rivers. Some companies try to use groundwater more than surface water because it is cleaner.
What is ground water?
Ground water is a little harder to understand than surface water because you can't actually see this water. Any water that is underground is groundwater. Half of the people in the United States use ground water for drinking water. In the water cycle, some of the precipitation sinks into the ground and goes intowatersheds, aquifers and springs. The amount of water that seeps into the ground depends on how steep the land is and what is under ground. For example: places that have lots of sand underground will allow more water to sink in than ones that have lots of rock. When the water seeps down, it will reach a layer of ground that already has water in it. That is the saturated zone. The highest point in the saturated zone is called the water table. The water table can raise and lower depending on seasons and rainfall. Groundwater flows through layers of sand, clay, rock, and gravel. This cleans the water. [Check out our sand and gravel filter experiment.] Because groundwater stays underground, things that fall into surface water can't fall into it. This means that groundwater stays cleaner than water on the surface. It has its problems, too. When farmers use fertilizers and insecticides, rain will wash them into the soil where they get into aquifers [groundwater]. Gas stations have big, underground tanks where they keep the gas. If these leak, the gas sinks into the groundwater, too. Groundwater doesn't need as much treatment as surface water, but it usually gets some because of these problems.
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