The Water Cycle
Evaporation, condensation, and precipitation
The water cycle (hydrological cycle) describes how water continuously moves through Earth's systems. Evaporation: the sun heats surface water, causing it to change from liquid to gas (water vapor) and rise into the atmosphere. Transpiration: plants release water vapor through their leaves. Condensation: as water vapor rises, it cools and condenses around tiny particles to form clouds (liquid water droplets). Precipitation: when cloud droplets combine and grow heavy enough, they fall as rain or snow. Collection: water collects in oceans, lakes, rivers, and groundwater. The cycle then repeats. The water on Earth today is the same water that has always been here — constantly recycled.
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Sign in →What is The Water Cycle?
Have you ever seen a puddle disappear on a sunny day? Where does all that water go? It does not vanish — it goes up into the sky! Water is always moving in a big circle called the water cycle. The Sun heats water in oceans, lakes, rivers, and puddles. When water warms up enough, it turns into an invisible gas called water vapor and floats up into the air. This is called evaporation — water turning into invisible water vapor gas. As the vapor rises higher, the air gets cooler. Cool air cannot hold as much invisible water vapor, so the vapor turns back into tiny liquid drops. Billions of tiny drops together make a cloud. This process is called condensation — air-water turning back into tiny water drops. When clouds collect enough drops, the water falls back down as rain or snow. That is called precipitation. The water lands on the ground, flows into streams and rivers, soaks into the soil, and eventually reaches the ocean — and then the whole cycle starts again! The same water has been going around this cycle for billions of years. The water you drink today might once have been drunk by a dinosaur.
Parameters explained
- Temperature(°C)
- Temperature tells how warm the air and water feel. When the temperature is higher, water can evaporate faster, which means more invisible water vapor rises into the air. That vapor can cool and help make clouds. When the temperature is lower, the water cycle may move more slowly. Try moving only this slider first. Watch the water, sky, and clouds, then describe what changed. This helps you see that heat from the Sun is an important part of evaporation, too.
- Rainfall(%)
- Rainfall tells how much water falls from the clouds back to Earth. A low rainfall setting means only a little rain comes down, like a dry day. A high rainfall setting means much more water falls, like a storm. Rain is part of precipitation, the step when water leaves clouds and returns to land, lakes, rivers, and oceans. Try keeping Temperature the same while changing Rainfall. Then explain where the falling water goes after it reaches the ground each time.
Common misconceptions
MisconceptionWater that evaporates is gone forever.
CorrectWater that evaporates does not disappear — it just changes form. Liquid water turns into invisible water vapor gas and rises into the air. It is still there, just not visible. When it cools down high in the sky, it turns back into tiny liquid drops and forms clouds. Then it falls as rain or snow and the whole journey starts over. The same water molecules have been cycling around Earth for billions of years.
MisconceptionClouds are made of water vapor (invisible water gas).
CorrectWater vapor is invisible — you cannot see it. Clouds are actually made of tiny liquid water droplets or tiny ice crystals that are so small and light they float in the air. You can see clouds because the tiny drops scatter light. Steam from a kettle looks white for the same reason — it is tiny droplets, not invisible vapor. The invisible water vapor gas turns into visible droplets when it cools — that is condensation.
MisconceptionRain comes from the ocean and nowhere else.
CorrectWater evaporates from many places — oceans, lakes, rivers, puddles, moist soil, and even plants. Plants release water vapor through tiny holes in their leaves in a process called transpiration. All of this vapor rises, condenses into clouds, and can fall as rain far inland — nowhere near the ocean. Rain that falls on mountains might have evaporated from a lake hundreds of kilometers away.
MisconceptionThe water cycle only works in warm places.
CorrectThe water cycle happens everywhere on Earth, including cold places. In very cold regions, water can fall as snow and build up as ice sheets or glaciers. Even ice slowly changes into vapor — called sublimation — without melting first. Melting snow and ice also contribute to rivers and groundwater. The water cycle is slower in cold regions but it never stops completely.
How teachers use this lab
- Use the Tropical preset to introduce evaporation, condensation, and precipitation, then have students identify visible evidence for each stage.
- Use the Desert preset to discuss why some regions receive less rain, then ask students to connect low rainfall to dry land and smaller collections of surface water.
- Use the Storm preset for a prediction activity: students explain what they expect to observe before heavy rain begins, then compare their prediction with the simulation.
- Have students keep Rainfall constant while changing Temperature, then record how warming or cooling affects what they observe in the water cycle.
- Have students keep Temperature constant while changing Rainfall, then write a claim about how water returns to land, rivers, lakes, and oceans.
Frequently asked questions
What makes water go up into the sky?
The Sun's heat gives water the energy it needs to evaporate — to turn from liquid water into invisible water vapor gas. When liquid water is warm enough, the tiny water molecules move fast and can escape into the air. Lighter than most of the air around them, these vapor molecules float upward. Wind also helps carry moisture higher. The higher the vapor rises, the cooler the air gets, and eventually the vapor condenses back into tiny drops. This is the engine of the water cycle. NGSS standard 2-ESS2-3 asks students to observe when small amounts of water evaporate and where it goes.
Is the water we drink the same water as dinosaurs drank?
Almost certainly yes! Earth does not make new water and does not lose its water into space. The water cycle keeps moving the same water around and around. Water evaporates, forms clouds, falls as rain, flows into rivers and oceans, evaporates again, and keeps going. Scientists estimate that Earth's water has been cycling for about 4 billion years. So the water in your glass today may have been in an ancient ocean, frozen in a glacier, or drunk by animals and people throughout history. The water cycle is one of the most important reasons Earth can support life for so long.
Why does it rain in some places but not others?
Rain requires two things: moist air (lots of water vapor) and something to cool that moist air so the vapor condenses into drops. Mountains are great at causing rain — when moist ocean air hits a mountain, it is pushed upward, cools, condenses, and rains on the mountain side. The air that comes down the other side has lost its moisture, so the far side of the mountain is often drier. Deserts are dry partly because the air there is very dry to begin with, or because the moist air from the ocean never reaches that far inland. Climate patterns, ocean currents, and geography all work together to decide where it is usually wet or dry.
Where does snow come from?
Snow forms when it is very cold high in the clouds. Water vapor or tiny droplets freeze directly into ice crystals. Each snowflake grows as more water vapor freezes onto it, building the six-sided crystal shapes that make snow look beautiful under a magnifying glass. Snowflakes fall when they get heavy enough, and if the air all the way down to the ground is cold enough, they reach the ground as snow instead of melting into rain. Snow that piles up in mountains melts in spring and provides water for rivers and farms.
What is groundwater and is it part of the water cycle?
Yes! When rain or melted snow soaks into the soil, some of it travels down through sand, soil, and cracks in rock until it collects in underground spaces. This underground water is called groundwater. It can stay underground for a short time or even thousands of years before it slowly flows to a river or spring and returns to the surface. People pump groundwater up through wells to drink and use on farms. Groundwater is an important part of the water cycle even though you cannot see it happening. NGSS standard 5-ESS2-1 asks students to describe how Earth's geosphere, hydrosphere, atmosphere, and biosphere are connected — and groundwater is a great example of water moving between systems.