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
What is surface water?
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
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?
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 into watersheds, 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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