Water on Earth is recycled through the water cycle. The water cycle is a series of continuous steps by which water is moved between living and nonliving parts of the environment. Water moves from bodies of water and the land to the atmosphere and then back to the land where it can be used by living things.

The processes of evaporation, condensation, precipitation, runoff, infiltration, and transpiration are all active in the water cycle.

The water cycle. The water moves through the environment.

The water cycle is continuous - there is no real beginning or ending point. The water cycle is the process by which water is continuously moved through the living and nonliving parts of the environment. Water is recycled in this manner. In the water cycle, water moves from the oceans, lakes, streams, land, and living things to the atmosphere and then back to Earth's surface.

The Sun is the driving force, or source of energy, for the water cycle.

The water cycle water moves from the atmosphere to Earth's surface and back again to the atmosphere in the water cycle. There is no beginning or ending point of the water cycle. It will continue as long as the Sun is still able to provide the source of energy for this process.

The Sun shines down on the ocean. The water on the surface evaporates. Evaporation is the process by which liquid water molecules absorb energy and are changed to water vapor.

This evaporation adds fresh water, in the form of water vapor, to the atmosphere.

Water evaporates from the oceans and large lakes. Smaller amounts of water evaporate from streams, puddles, the soil, and from the surface of your skin. Water is constantly entering the atmosphere through the process of evaporation.

When water evaporates, the molecules on the surface absorb energy from the Sun. These molecules, with their added energy, change into water vapor and escape into the atmosphere.

Plants play an important role in the water cycle as well. Plants take water from the soil into their roots. The water passes through the plant and eventually is given off from the surface of the leaves. This process is called transpiration.

Water loses water vapor to the atmosphere through the process of transpiration. This is one example of how living organisms contribute to the movement of water in the water cycle.

Water vapor in the atmosphere will rise upward on warm air currents. The air will cool as it rises. Cooler air can hold less water than warmer air. Therefore the water vapor will cool and return to the liquid state. This process is called condensation.

Condensation in the atmosphere leads to the formation of clouds. Often water droplets that have condensed will gather around a small dust particle in the atmosphere. This forms clouds.

These clouds in the atmosphere eventually become heavy with moisture. The water then falls to the surface of Earth as precipitation. This can be in the form of snow, sleet, rain, or hail.

It is believed that about 10 days elapse between the evaporation of a water droplet and the return of that droplet to Earth in the form of precipitation.

Most precipitation falls on the oceans. This makes sense since nearly 75% of Earth's surface is covered in oceans.

The water in the ocean could stay there for several years before evaporating back up into the atmosphere. The cycle then continues.

There are several options for water that falls on Earth's surface. Some of this water will form shallow puddles and evaporate back to the atmosphere almost immediately.

Some precipitation may fall on impermeable surface. This may be a sidewalk, parking lot, or other hard layer. This water then moves as runoff. Water that moves as runoff flows downhill and eventually makes it to a larger body of water. Eventually, this water will make its way back to the ocean.

Water moving along the surface will travel along areas that are hard packed or that have been paved. This water moves downhill until it enters into a large body of water, such as a stream, lake, or ocean.

Still more precipitation that falls may infiltrate into the soil and become part of the groundwater.

Groundwater is the water that fills the cracks and pores in the rock layers and soil underground. Groundwater slowly flows downhill to large bodies of water. Often, groundwater is a source of drinking water for many. Wells are dug into the groundwater and the water pumped out. The water is replaced by infiltration.

The soil or rocks underground have different layers. Some layers are able to hold water. These layers are permeable and porous. Pores are the spaces between particles in the soil or rock. A rock is permeable if water is able to pass through it. Some rock or soil layers are impermeable. Water cannot pass through these. As water infiltrates into the ground, the water will pass through the permeable layer. It will not be able to pass through an impermeable layer and the water will start to fill up the permeable layer.
The area that is filled with water is called the saturated zone. The area above this that does not contain water in the pore space is the unsaturated zone. The boundary between the saturated and unsaturated zones is called the water table.

A well must be dug deep into saturated zones. The water table fluctuates depending upon the amount of precipitation. During times of drought, the water table will drop. If there is a lot of precipitation, the water table will rise.

The water cycle can also serve as a filter to water. Consider the difference between water that falls to the ground and becomes runoff and water that may infiltrate into groundwater.

Surface runoff water may pick up contaminants along the way. Gasoline, fertilizers, or other pollutants will be picked up by the water as it runs along the surface. The water does not have the opportunity to become clean. There is the possibility that larger bodies of water, such as a lake or the ocean, will become polluted with this contaminated ground water.

Water that infiltrates into the groundwater has a better chance of being purified. This water moves slowly through the pores of the soil or rock. This slow movement through very small pore spaces allows the contaminants that may be contained in the water to be filtered.

Fun fact: There is water in the atmosphere. Some estimates put the amount of water in the atmosphere at any one time at about 3,100 cubic miles of water. Does that sound like a lot? If all this water were to fall onto Earth's surface at the same time, it would only create a worldwide puddle of about 1 inch!