The water on Earth today is the same water that fell as rain on ancient forests, filled oceans before dinosaurs, and carved out the Grand Canyon. Water doesn’t disappear. It moves through a continuous cycle that shapes weather, sustains every living thing, and determines whether communities have enough to drink.
The water cycle is the continuous movement of water on, above, and below the surface of the Earth. Water changes between three physical states — liquid, solid (ice), and gas (water vapor) — as it moves through the cycle. The same amount of water has existed on Earth for billions of years. It just keeps moving.
The cycle is powered by two forces: energy from the sun, which causes water to evaporate, and gravity, which pulls water back down as precipitation and causes it to flow through rivers, streams, and underground aquifers.
Understanding the water cycle matters because every community on Earth depends on it for fresh water. When the cycle works, rain falls, rivers flow, wells fill, and people have water to drink. When any part of the cycle is disrupted — by drought, pollution, or climate change — communities lose access to water they need to survive.
Liquid water, solid ice, and gaseous water vapor.
Solar energy powers evaporation; gravity powers precipitation and flow.
Every stage is happening somewhere on Earth right now.
Water moves through six main stages in the cycle. These stages happen simultaneously all over the planet, not in sequence.
Heat from the sun causes liquid water to become water vapor, a gas. Most evaporation happens from oceans, lakes, and rivers. Plants also release water vapor through a similar process called transpiration. Together, evaporation and transpiration are sometimes called evapotranspiration.
As water vapor rises into cooler parts of the atmosphere, it condenses back into tiny liquid droplets. These droplets cluster together around particles of dust or pollen in the air, forming clouds.
When the water droplets in clouds become too heavy to stay suspended, gravity pulls them down as precipitation. Depending on the temperature, precipitation falls as rain, snow, sleet, or hail.
Some precipitation soaks into the ground. This water moves through layers of soil and rock until it reaches an underground layer of saturated earth called an aquifer. Groundwater stored in aquifers supplies the wells that billions of people depend on for drinking water.
Precipitation that doesn’t soak into the ground flows across the surface of the Earth. Gravity pulls this runoff downhill, where it forms streams, rivers, and eventually returns to lakes and oceans.
Water collects in oceans, lakes, rivers, and underground aquifers. From these reservoirs, the cycle starts again as water evaporates back into the atmosphere.
A complete view of all six stages. Save, print, or project for classroom use.
The water cycle moves water continuously between oceans, atmosphere, land, and groundwater. Source: The Water Project, adapted from USGS.
Key terms students will encounter when studying the water cycle.
Hands-on activities that demonstrate water cycle concepts. Most use materials found in a classroom or home.
How is this like what happens on Earth? What’s the “sun” powering evaporation? Where is “precipitation” happening?
Water vapor from the hot water rises. When it meets the cold air from the ice, it condenses around the smoke particles, forming a visible cloud.
How does this compare to how rain becomes groundwater? Why is natural filtration important for drinking water? What happens when pollution contaminates the soil layer?
More from The Water Project classroom library
The water cycle works continuously across the planet, but it doesn’t deliver water equally. And when something disrupts the cycle — drought, pollution, conflict, infrastructure collapse — entire communities lose access to clean water.
The Water Project works in Kenya, Sierra Leone, and Uganda, where water cycle disruptions have real daily consequences. Here’s what that actually looks like:
In Southeast Kenya, rains that used to arrive on predictable seasonal schedules now come late, skip seasons entirely, or fall in damaging bursts. A farmer planning crops around April rains may find them arriving in June. A community that stored rainwater during the wet season may run out before the next rains arrive. The water cycle still works — but its timing no longer matches what communities built their lives around.
How The Water Project works in KenyaWhen water tables fall, hand-dug wells that communities have depended on for generations go dry. In Sierra Leone, our teams drill deeper borehole wells directly into existing dry wells to reach groundwater below the current water table. The cycle is still delivering water to the aquifer — it’s just lower than it used to be.
How The Water Project works in Sierra LeoneRunoff that flows over contaminated land carries pollution into rivers, streams, and eventually drinking water supplies. In communities without water treatment infrastructure, runoff-polluted water causes disease outbreaks. Cholera, typhoid, and dysentery are transmitted through water that looks clean but carries pathogens from contaminated runoff.
Even when the water cycle delivers water to a region, it doesn’t always deliver it near where people live. In rural areas across sub-Saharan Africa, the nearest water collection point — a spring, a river, a distant well — can be hours away on foot. Women and children carry water by hand over long distances. That’s labor the water cycle doesn’t account for, but daily life depends on it.
Climate change is intensifying the water cycle. Here’s what scientists observe.
A warmer atmosphere can hold about 7% more water vapor per degree Celsius of warming. This means more intense precipitation events in some regions.
Other regions receive less rain more frequently, as shifting atmospheric patterns move precipitation away from traditional zones.
Mountain glaciers that have acted as natural water reservoirs for downstream communities are shrinking. Communities in Nepal, Peru, and the Alps face changing seasonal water availability as glacial meltwater patterns shift.
Saltwater intrusion contaminates freshwater sources in low-lying coastal regions, affecting drinking water and agriculture.
Higher temperatures accelerate evaporation, drying soils faster and stressing crops even in places where total rainfall hasn’t changed.
For communities in water-stressed regions, these changes are already compounding existing challenges. Climate change doesn’t break the water cycle — it’s making it deliver water less predictably, less equitably, and in larger swings between too much and too little.
The Water Project’s work is designed to help communities adapt to their part of the water cycle. Each solution works with a natural stage — not around it.
Natural springs deliver groundwater to the surface year-round. Our teams protect these springs by building infrastructure that keeps contaminated runoff from mixing with the spring water. The water cycle already delivers clean groundwater — the project simply makes it safer to access.
Works with collectionIn communities where the water table has fallen, drilled boreholes reach groundwater deeper than hand-dug wells can access. This works with the cycle by tapping into water that has infiltrated over time.
Works with infiltrationIn Southeast Kenya’s semi-arid regions, rainwater harvesting tanks capture precipitation during wet seasons and store it for use during dry months. Large tanks at schools can hold up to 104,000 liters — enough to provide clean water on school grounds for months after rains end.
Works with precipitationSand dams are concrete walls built across seasonal rivers. They capture sand and water during flash floods, and the sand stores water that communities can access for months afterward. Sand dams work with the natural runoff cycle to create water storage in places where above-ground storage evaporates too quickly.
Works with runoffUnderstanding the water cycle is the first step. Here are ways students can apply that knowledge.
Take the Water Challenge or start a fundraiser with your class. Your action connects real communities to the water cycle they depend on.
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