Water is constantly moving within and around the earth in a continuous pattern called the hydrologic cycle.

Cycle with Water
Use the navigation buttons on the right to explore the water cycle. Using the oval buttons, you can see the three primary stages of the water cycle in action. Then check out the processes that make up these stages by using the rectangular buttons.

Although such rivers as the Mississippi River may seem huge to us, they are a very small part of the entire hydrologic cycle. Note that only about 0.2% of the water is located in rivers, lakes, or the atmosphere.

The earth’s supply of water remains constant, however, people can effect the quantity and quality available. Large cities accelerate water drainage rates through road drains and city sewer systems. This changes the rates of infiltration, evaporation, and transpiration that would normally occur.

Evaporation
The sun’s energy heats up water from oceans, lakes, ponds, rivers and causes it to evaporate. In addition, water absorbed by plants pass through them and then transpires through the leaves to the air and changes it into water vapor. The water vapor rises then cools and condenses to form clouds.

Condensation
Clouds hold the water temporarily as vapor, small liquid droplets, or little ice particles. When cloud temperatures become cold enough, moisture vapor cools and condenses.

Precipitation
The condensed water within clouds forms larger liquid drops or solid moisture particles and is pulled to earth by gravity as precipitation in the form of rain or snow. Some of this rain or snow is absorbed by the ground (infiltration) and then becomes groundwater (0.6%). Most of this water return to the ocean. Some water runs off the surface of the ground and becomes nonpoint runoff to streams and rivers, finally returning to the ocean. A very small amount (2%) of the precipitation falls in colder areas of the earth as snow and becomes tied up for longer periods of time in glaciers and ice caps.