Water is essential to life. Without it, the biosphere that exists on the surface of the earth wouldn't be possible. Nicknamed the "water" planet, Earth is covered by one of our most precious resources. However, almost 93% is locked in the oceans, toxic to humans and many plants and animals. How do we obtain fresh water resources then? Where does drinkable water come from? To understand, we need to turn to the Hydrologic Cycle. Water's molecular arrangement is very simple, two hydrogens to each oxygen atoms, but this is misleading. Water has many unique properties that allow it to be such a universal material. One special characteristic of water is its ability to change state very easily under Earth conditions. It can be found readily on the planet in all of its three forms, solid, liquid, and gas. These forms also play a great part in the hydrologic cycle. Now, exactly what is the hydrologic cycle.? The hydrologic cycle takes place in the hydrosphere,this is the region containing all the water in the atmosphere and on the surface of the earth. The cycle is the movement of water through this hydrosphere. Now the entire process is very simple, divided in to five parts CondensationInfiltration Runoff Evaporation Precipitation The process begins with condensation, when water vapor condenses in the atmosphere to form clouds. Condensation occurs when the temperature of the air or earth changes. Water changes states when temperatures fluctuate. So when the air cools enough, water vapor has to condense on particles in the air to form clouds. This process is very noticeable on plants as they dew in the morning. As clouds form, winds move them across the globe, spreading out the water vapor. When eventually the clouds can't hold the moisture, they release it in the form of precipitation, which can be snow, rain, hail, etc. The next three stages: infiltration, runoff, and evaporation occur simultaneously. Infiltration occurs when precipitation seeps into the ground. This depends a lot on the permeability of the ground. Permeability is the measure of how easily something flows through a substance.The more permeable, the more precipitation seeps into the ground. If precipitation occurs faster than it can infiltrate the ground, it becomes runoff. Runoff remains on the surface and flows into streams, rivers, and eventually large bodies such as lakes or the ocean. Infiltrated groundwater moves similarily as it recharges rivers and heads towards large bodies of water. As both of these processes are happening, the power of the sun is driving this cycle by causing evaporation. Evaporation is the change of liquid water to a vapor. Sunlight aids this process as it raises the temperature of liquid water in oceans and lakes. As the liquid heats, molecule are released and change into a gas. Warm air rises up into the atmosphere and becomes the vapor involved in condensation. Considering so little of the water on earth is drinkable to people, it is amazing the supply has survived as long as it has. The hydrologic cycle continues to move water and keep sources fresh. It is estimated that 100 million billion gallons a year are cycled through this process. Without this process life on Earth would be impossible. We need it to sustain us and for all of our life processes to function. Without water, life would not be possible on Earth. Images provide by "Great Lakes Info" of Environmental Canada, Bob Dvorak, and   The Challenge This lesson is just the tip of the iceberg. To understand the hydrologic cycle, one must learn and study the water and its action in his/her own area. Earthscape challenges viewers to go out into their regions and learn more about the Hydrologic Cycle. View your area and determine where water is located. Is this water fresh or saltwater? Where does your community get its drinking water? How is drinking water obtained? Examine which processes of the Hydrologic Cycle are in motion right now. For further activities dealing with water, check out our Hands-on Activities section in the Water module. We challenge you to become aware of water in your region. Question For Further Thought.. What would happen to the planet if the hydrologic cycle stopped functioning? What would happen to societies as the supplies of water diminished? Would our planet die? What would happen if the polar icecaps melted and the hydrologic cycle couldn't keep water levels stable? Where would we go as water levels rose out of control? Could we ever use the ocean to supplement or water once freshwater disappears? What ways could the oceans be used to provide us with a source of water? Disclaimer and Copyrig