The water cycle, also called the hydrologic cycle, is the continual movement of water between the ocean, atmosphere, land, rivers, living organisms, and underground stores. The Sun supplies much of the energy for evaporation; gravity helps move rain, rivers, and groundwater. There is no single beginning or end. USGS overview.

You may have learned an easy sequence: evaporation → condensation → precipitation. That is a useful introduction, but real water does not always follow only those three steps. Some water runs into rivers, some enters the soil, and some passes through plants. Explore the three paths in the interactive 3D landscape above.

How to use the interactive 3D model above

Select Surface water, Groundwater, or Through plants. Press Play to follow a highlighted representative water pathway, use Next and Previous to learn one process at a time, and rotate the landscape with a mouse, touch gesture, or arrow keys. A cluster of small blue droplet-shaped markers follows a conceptual water pathway, not a literal visible water molecule or visible water vapor. During precipitation only, small animated raindrops fade in and out. During evaporation/transpiration, tiny pale symbols represent invisible water vapor, not real visible gas; blue liquid markers gather again during condensation. Small real raindrops are mostly rounded, while larger falling drops become flatter, not pointy teardrops NASA GPM. All movements and timings remain schematic, not measured weather predictions.

1. Evaporation: liquid water becomes invisible vapor

Energy from sunlight helps water molecules escape from liquid water at oceans, lakes, soil, and other wet surfaces. The molecules enter the air as water vapor, a gas we cannot see. Water does not have to boil at 100 °C to evaporate; evaporation can occur at ordinary outdoor temperatures. The ocean is an important source of evaporation, but evaporation can happen wherever exposed liquid water is present. USGS water cycle.

Common misconception: The white shape above a kettle is not invisible water vapor itself. What you can see is mostly tiny liquid droplets that formed when vapor cooled and condensed.

2. Condensation: water vapor can form cloud droplets

Air carrying water vapor may rise and cool. Under suitable conditions, vapor condenses on microscopic airborne particles, producing tiny liquid droplets; cold clouds can also contain ice crystals. The visible cloud is made of tiny droplets and/or ice crystals, not an opaque mass of gaseous water vapor. Clouds can appear, change, and disappear because condensation and evaporation continue in moving air. NOAA: How clouds form.

3. Precipitation: water returns from clouds

Droplets or ice particles in clouds can grow large enough to fall under gravity. This is precipitation: rain, snow, sleet, or hail depending on conditions. Precipitation falls over oceans as well as land; our small scene follows selected pathways toward land so that other processes are easier to inspect. It does not imply all rain falls on mountains. NOAA: Hydrologic cycle.

4. Surface runoff and rivers: water moves downhill

After rain, water may flow over ground, into streams and rivers, and ultimately toward lakes or the sea. This is surface runoff followed by streamflow. In the scene, a small winding blue stream and moving water markers show a path downhill toward the ocean. The amount of runoff depends on rainfall, soil, slope, vegetation, and how much water has already entered or saturated the ground. Not every drop reaches the ocean immediately: water can remain in wetlands, reservoirs, lakes, vegetation, or other stores. USGS overview.

5. Infiltration: part of the rain enters the soil

Some precipitation soaks into the soil through infiltration. Water may be held as soil moisture, taken up by roots, move deeper to recharge an aquifer, or eventually move sideways to a stream or spring. Infiltration is not the same as groundwater recharge: water that entered soil does not automatically reach a deep aquifer. The downward and underground routes can take very different lengths of time. An arrow in the soil cutaway depicts infiltration; a separate slow route illustrates one possible groundwater pathway toward the ocean. Groundwater can also feed springs, rivers, or aquifers and does not travel as an open underground river. USGS: Infiltration and the water cycle.

6. Plants: root uptake and transpiration

Plant roots absorb some soil water. Plants use and transport this water, and some escapes from leaves as water vapor through transpiration. Evaporation from soil and transpiration from plants together contribute to evapotranspiration. The scene's plant route shows one plausible connection from soil water back to the atmosphere, not the only outcome for water taken up by plants. USGS overview.

Why the water cycle matters

The cycle continually redistributes water and helps connect weather, rivers, ecosystems, agriculture, and water supplies. People can also change the pathways by pumping groundwater, building reservoirs, changing land cover, and using water for farming or industry. The total amount in any individual lake, river, or aquifer can rise or fall even though Earth keeps cycling its water. USGS 2022/2023 water-cycle diagram.

Questions students often ask

Does the water cycle start at the ocean?

No. We often start a drawing at the ocean for convenience, but water can enter or leave many different stores; a cycle does not have a fixed starting point.

Is a cloud made of steam?

A visible cloud contains microscopic droplets and/or ice crystals. Water vapor itself is invisible. NOAA cloud explanation.

Does all rainwater become groundwater?

No. Some becomes runoff, some is taken up by plants, some evaporates again, and some enters soil. Of the water entering soil, only a portion may recharge groundwater. USGS infiltration explanation.

What does the cluster of blue droplets mean?

The many blue droplets are stylized pathway markers, not actual droplets floating everywhere in nature. They help you follow movement between stores. Water vapor is an invisible gas; the tiny falling particles in the separate shower illustrate liquid rain. Paths and durations are simplified for learning.

Sources and model limitations

This explanation and the schematic 3D model follow the USGS Water Science School, USGS infiltration overview, and NOAA on cloud formation. The interactive scene is not a numerical hydrology model: it does not calculate real evaporation rates, cloud microphysics, rainfall probability, aquifer discharge, conservation of measured water volumes, or elapsed geological/hydrological time. A complete global water cycle also includes snow, ice, sublimation, ocean precipitation, and human impacts that this short scene does not animate.