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Home page for the Water Cycle topic.This website, presented by NASA's Global Precipitation Measurement (GPM) mission, provides students and educators with resources to learn about Earth's water cycle, weather and climate, and the technology and societal applications of studying them.

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WATER IS WATER: A BOOK ABOUT THE WATER CYCLE | BY MIRANDA PAUL | READ ALOUD

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Note: Our information only covers the natural water cycle, which does not take human activities into account. In today's world, humans have a major impact on many components of the water cycle.
Access in-depth information about each component of the water cycle:
A (very) quick summary of the water cycle

Where does all the Earth's water come from? Primordial Earth was an incandescent globe made of magma, but all magmas contain water. Water set free by magma began to cool down the Earth's atmosphere, until it could stay on the surface as a . Volcanic activity kept and still keeps introducing water in the atmosphere, thus increasing the surface- and groundwater volume of the Earth.

The water cycle has no starting point. But, we'll begin in the , since that is where most of Earth's water exists. The sun, which drives the water cycle, heats water in the oceans. Some of it evaporates as into the air. Ice and snow can directly into water vapor. Rising air currents take the vapor up into the atmosphere, along with water from evapotranspiration, which is water transpired from plants and evaporated from the soil. The vapor rises into the air where cooler temperatures cause it to condense into clouds.

Air currents move clouds around the globe, cloud particles collide, grow, and fall out of the sky as precipitation. Some precipitation falls as snow and can accumulate as ice caps and glaciers, which can store frozen water for thousands of years. Snowpacks in warmer climates often thaw and melt when spring arrives, and the melted water flows overland as snowmelt.

Most precipitation falls back into the oceans or onto land, where, due to gravity, the precipitation flows over the ground as surface runoff. A portion of runoff enters rivers in valleys in the landscape, with streamflow moving water towards the oceans. Runoff, and groundwater seepage, accumulate and are stored as freshwater in lakes. Not all runoff flows into rivers, though. Much of it soaks into the ground as infiltration. Some water infiltrates deep into the ground and replenishes aquifers (saturated subsurface rock), which store huge amounts of freshwater for long periods of time.

Some infiltration stays close to the land surface and can seep back into surface-water bodies (and the ocean) as groundwater discharge, and some groundwater finds openings in the land surface and emerges as freshwater springs. Over time, though, all of this water keeps moving, some to reenter the ocean, where the water cycle "ends" ... oops - I mean, where it "begins."

Global water distribution

For an estimated explanation of where Earth's water exists, look at the chart below. By now, you know that the water cycle describes the movement of Earth's water, so realize that the chart and table below represent the presence of Earth's water at a single point in time. If you check back in a thousand or million years, no doubt these numbers will be different!

Notice how of the world's total water supply of about 333 million cubic miles (1,386 million cubic kilometers) of water, over 96 percent is . And, of the total freshwater, over 68 percent is locked up in ice and glaciers. Another 30 percent of freshwater is in the ground. Thus, rivers and lakes that supply surface water for human uses only constitute about 22,300 cubic miles (93,100 cubic kilometers), which is about 0.007 percent of total water, yet rivers are the source of most of the water people use.
One estimate of global water distribution Source: Igor Shiklomanov's chapter "World fresh water resources" in Peter H. Gleick (editor), 1993, Water in Crisis: A Guide to the World's Fresh Water Resources (Oxford University Press, New York).
(Percents are rounded, so will not add to 100)

# data[].attributes.attachment_link.description
Note: Our information only covers the natural water cycle, which does not take human activities into account. In today's world, humans have a major impact on many components of the water cycle. Access in-depth information about each component of the water cycle: Where does all the Earth's water come from?

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Learn about how water moves all around our planet.

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Sing, dance, and learn all about the water cycle!