Earth's+Water

=Water Found on Earth= If you look at the Earth from space it looks like a blue ball because three-fourths or about 70% of the Earth is covered in water. The Earth is the only planet in our solar system that where scientists have found oceans, rivers, and lakes. Water makes life on Earth possible because all living organisms need water in order to stay alive and healthy. People use water for drinking, cooking, bathing, and as a healthy drink. Many foods come from oceans, rivers, and lakes. In addition, people use water found on Earth to ship products between locations and put dams on rivers to turn moving water into electricity to produce energy. Water is also used for leisure. Sports such as swimming, surfing, skiing, boating, and iceskating would not be possible without water. Almost all the water, ninety-seven percent, of water on Earth is salt water. Most salt water is found in the four main oceans which are the Pacific, Atlantic, Indian, and Arctic. Some salt water is found in lakes. Most lakes contain fresh water, but a few lakes contain salt water. Mono Lake in California and Great Salt Lake in Utah are two large saltwater lakes in the United States. Water is carried to the oceans by rivers. The river meets an ocean at an estuary. At the estuary fresh water from the river mixes with salt water from the oceans.

Salt water is filled with salt and other minerals which makes it undrinkable for humans. Although the salt can be removed, it is an expensive process. Graph from U.S. Geological Survey

Fresh Water
On Earth about three gallons of every 100 gallons of water is fresh water. Less than 1% of all water on Earth is fresh water that humans can actually use. We use this small amount of fresh water for drinking, transportation, heating and cooling, industry, and many other purposes. Most fresh water, about sixty-nine percent, is frozen in glaciers and in ice caps or sheets. Most of Earth's fresh water is found in these glaciers, ice caps, and sheets. Lakes, ponds, and rivers hold a small percent of Earth's fresh water. The water found in lakes, ponds, and rivers is called surface water. Rivers carry this fresh water to the ocean. Sooner or later all the fresh water in rivers ends up in the ocean.

Earth's fresh water is also found in the ground. This water is called groundwater. Almost one-fourth of the Earth's fresh water is groundwater. No matter where on Earth you are standing at some depth below you the ground is saturated with water. Water becomes groundwater when rainwater and water from melting snow and ice soak into the ground. The soil absorbs this water. The top layer of soil on Earth is made of small bits of rock, dead plants, and animal materials that cause the soil to be porous. Things that are porous can absorb water. Groundwater slowly fills in air spaces and gaps in soil and rocks and then spreads. The groundwater goes deep into the ground for thousands of meters in some places. The water table is the highest level of soil and rock that is completely filled with groundwater.

Plants are another place where fresh water is located. A plant takes water from the soil through its roots and then the water travels up the stem and into the leaves of plants. Plants use the sun's energy and water to make their own food by mixing water with carbon dioxide in a process called photosynthesis. Water not used by the plant escapes through tiny holes in the leaves. The water goes into the air, in a process called transpiration, as a gas.

Freshwater is also found in the atmosphere in the form of water vapor. Air has a different amount of water vapor in it. When the air has only a small amount of water vapor the air feels dry. When air has a lot of water vapor in it the air feels damp. Clouds also contain fresh water that is brought to them through the process of evaporation and transpiration.

What is Water Made Of
Water is made of atoms, the smallest partical of an element, like oxygen or hydrogen. Atoms join togther to form molecules. A water molecule has two hydrogen atoms (H) atoms and one oxygen atom (O). That's why water is sometimes refered to H20.

Water Treatment
Water treatment is the process of cleaning water to make it usable and safe. Water picks up natural pollutants because it is a solvent. In nature water is not always clean enough for people to drink so it has to be treated. In the 1850s germs were seen in water for the first time through a microscope. In 1902, Belgium was the first country to use chlorine to clean and treat the publics water supply. Today, almost all cities in the world treat their drinking water.