The Water Cycle explains interactions between the atmosphere, hydrosphere, and lithosphere.  Evaporation of water from the oceans, seas, rivers, and streams into the atmosphere produces precipitation.

Water is a transparent, odorless, tasteless liquid composed of the elements hydrogen and oxygen. It is a very good solvent, meaning that many substances can dissolve in it easily.  Water is important to our lives, and without it we could not live.  In fact, there are no living creatures that can live without water.  Water most probably originated on this planet as gases were being emitted from volcanoes.  The Earth's atmosphere captured this water and has continuously recycled it throughout time, in what is called the water cycle.  Water evaporates and forms clouds; the clouds provide rain and snow, which is collected in rivers, lakes, underground reservoirs, and oceans that are the source for further evaporation.  Water is that perfect substance for the water cycle, because it has a high boiling point and a low freezing point.

Water's surface tension (the ability of a substance to stick to itself) makes it an excellent substance to float heavy objects upon.  Water not only sticks to itself, but also to other surfaces, and this allows it to move against gravity, which is very important to plants when transporting water form the soil to their leaves.  This upward motion is known as capillarity or capillary movement.
The Earth is made up of both land and water.  When water is heated it changes from the  liquid to the gas water vapor.  This process is called evaporation.  When water vapor is cooled, as it would be if it were taken higher in the atmosphere, this gas will condense, or change back to liquid form.

We can see water vapor condensing when we watch clouds.  A cloud is nothing more than water vapor that has condensed back to a liquid form.  A cloud is made of extremely tiny drops of water which can remain suspended in the air.  As a cloud grows, and more and more water condense in the same place, the cloud droplets get larger.  Eventually, these cloud droplets will be too large to remain in the air.  The cloud is then said to be saturated.  A saturated cloud will usually precipitate its excess water, or cause it to fall.  This is how it rains or snows.  Moisture falling from clouds is called precipitation.

The amount of the gaseous water vapor that is in the air tells us the relative humidity of the air.  Humidity is a measure of how moist or dry feeling the air is.  When the air is warm, it can hold more water vapor than when it is cold.  When the humidity is high, it is very difficult to dry off after swimming, since there is so much moisture already in the air, it is not easy for more to evaporate.  When the humidity is low, dry air easily evaporates water. 

The cycle of evaporation, condensation, and precipitation of water is called the water or hydrologic cycle.   Since clouds move across the sky, the precipitation does not usually fall in the same place that the water came from.  This is how the earth spreads water across land areas and allow us to live in so many different areas.

The hydrologic or water cycle is a major driving force on our planet.  Water is in constant motion, evaporating into the atmosphere to and from oceans, lakes, rivers, and streams.  When the atmosphere can no longer support the moisture within the clouds we experience rain, snow, hail, or sleet.  Some water  is locked in the form of ice at the polar caps and in  glaciers. Water is returned to the system through drainage, which results from the melting of snow that has accumulated during the winter months.  This water flows on the surface of the Earth and percolates through the Earth as groundwater. Water is not actually consumed but is continuously recycled.    When water is heated, it changes from the  liquid to the gas water vapor.  This process is called evaporation.  When water vapor is cooled, as it would be if it were taken higher in the atmosphere, this gas will condense, or change back to liquid form.

We can see water vapor condensing when we watch clouds.  A cloud is nothing more than water vapor that has condensed back to a liquid form.  A cloud is made of extremely tiny drops of water which can remain suspended in the air. A cloud is a colloid, or 2 states of matter (liquid and air).  As a cloud grows, and more and more water condense in the same place, the cloud droplets get larger.  Eventually, these cloud droplets will be too large to remain in the air.  The cloud is then said to be saturated.  A saturated cloud will usually precipitate its excess water, or cause it to fall.  This is how it rains or snows.  Moisture falling from clouds is called precipitation.

The cycle of evaporation, condensation, and precipitation of water is called the water or hydrologic cycle.   Since clouds move across the sky, the precipitation does not usually fall in the same place that the water came from.  This is how the Earth spreads water across land areas and allows us to live in so many different areas.