The water cycle is the continuous movement of water between the oceans, the air and the land, powered by energy from the Sun and pulled back down by gravity. Water evaporates from oceans, lakes and soil, and plants release more through transpiration. The vapour rises, cools and condenses into the tiny droplets and ice crystals that make clouds. When those grow heavy enough they fall as precipitation: rain, snow, sleet or hail. On land the water either soaks in (infiltration), flows over the surface into rivers (runoff), or is stored as ice and groundwater, and eventually it reaches the sea or the air again. The total amount of water barely changes. It just keeps moving between stores.

Stores and flows: the two words that organise everything

The cleanest way to understand the cycle, and the way most exam mark schemes think about it, is as a set of stores (places where water is held) connected by flows (processes that move water from one store to another). Every arrow on a water cycle diagram is a flow. Every labelled place is a store.

Where the water actually is, using the figures the US Geological Survey publishes:

Two things follow from that table. Fresh water you can easily use is a tiny fraction of the total. And the atmosphere holds very little water at any moment, yet moves an enormous amount, because water passes through it so quickly. A molecule might spend three thousand years in the Pacific and nine days in the sky.

The main processes, in order

There is no real starting point, but most explanations start at the ocean because that is where most evaporation happens.

Evaporation and transpiration are often added together as evapotranspiration, because from a satellite you cannot easily tell which one a given bit of vapour came from. USGS estimates that plants supply roughly a tenth of the moisture in the atmosphere, and most of the rest comes from oceans, seas, lakes and rivers.

Why air cools as it rises

This is the step students most often skip, and it is the one that explains clouds. Air pressure falls with height. A rising pocket of air expands as the pressure around it drops, and expanding air cools. Cool air can hold less water vapour than warm air, so once it cools to its dew point, vapour starts condensing onto tiny particles in the air (condensation nuclei). That is why clouds form over mountains, along weather fronts, and on hot afternoons when warm air near the ground rises in columns.

Two energy facts worth one sentence each

Evaporation takes in a lot of heat, which is why sweat cools you. Condensation releases that same heat back into the air, which is part of what powers thunderstorms. A higher-level answer mentions both: the water cycle moves heat around the planet, not only water.

What goes wrong on most diagrams

Teachers see the same mistakes every year. Fix these and you are ahead of most of the class.

• "Clouds are water vapour." They are not. Vapour is invisible. Clouds are liquid droplets or ice crystals, which is why you can see them.
• Evaporation drawn only from the sea. Lakes, wet soil and puddles evaporate too, and plants transpire. A diagram with one arrow up from the ocean is incomplete.
• Rain going straight into the river. On most land it first infiltrates or runs off, and much of it reaches rivers slowly, through groundwater. That slow route is why rivers keep flowing in dry weeks.
• Arrows pointing the wrong way. Transpiration goes up out of leaves, not down into them. Infiltration goes down. Check every arrow.
• Forgetting people. Paving, drainage and cutting down forests change the cycle. Concrete stops infiltration and increases runoff, which is a big reason towns flood. Removing forest reduces transpiration, which can reduce local rainfall.
• "New water." The cycle recycles water. The amount on Earth is effectively fixed over human timescales; what changes is where it is and in which state.

Worked example: a three minute class script

Here is a script of about 300 words: two minutes at 150 spoken words a minute, closer to three once each drawing has time to build. It follows the cycle from one named starting point, which is how a cycle should be explained, and it ends with a human consequence, which is what teachers most often say is missing. Each paragraph is one scene.

Scene 1, the whole loop. "The water cycle is how water moves between the ocean, the air and the land, driven by the Sun and pulled back down by gravity. Let's follow one drop of water around it."

Scene 2, evaporation. "Our drop starts in the Atlantic. Sunlight warms the surface, and the drop evaporates. It becomes water vapour, an invisible gas, and rises with the warm air. Most of the vapour in the sky starts like this, from the ocean."

Scene 3, transpiration. "Over land, plants add more. A tree pulls water up from its roots and releases it as vapour through tiny pores in its leaves called stomata. That is transpiration."

Scene 4, condensation. "As the air rises, it expands and cools. Cool air holds less vapour, so the vapour condenses onto specks of dust and salt, forming tiny droplets. Billions of them make a cloud. A cloud is liquid water, not vapour."

Scene 5, precipitation. "Inside the cloud, droplets bump together and grow. When they are too heavy to stay up, gravity wins, and they fall as rain, or as snow if it is cold enough."

Scene 6, infiltration and runoff. "Our drop lands on a hillside. If the soil is loose, it soaks in. That is infiltration. It may sink further and join groundwater, moving slowly underground for months. If the ground is hard or already soaked, it runs over the surface into a stream. That is runoff."

Scene 7, collection. "Either way, gravity carries it downhill, into a river, and back to the sea. The loop is complete, and it can start again."

Scene 8, why it matters. "In towns, roads and roofs stop water soaking in, so more of it runs off at once. Heavy rain reaches the rivers in hours instead of weeks, and that is one reason cities flood. Understanding the water cycle is how engineers design drains, parks and reservoirs that work with it."

The drawing for each scene adds to the one before, so by scene 7 the viewer has built the whole diagram in the right order. That build-up is the point of a drawn explainer: a finished diagram shown all at once is just a poster.

Make your own version for class

If you are making this for a project rather than revision, the general advice in how to make a science explainer video for class applies, and the water cycle is a textbook example of the "cycle" shape it describes. If the brief is about human impact (floods, drought, deforestation), use the evidence-based structure in how to make an environmental science video project instead, which asks for real measured numbers and a response.

1. 1

   Pick a named starting point

   Start the drop somewhere specific, an ocean, a named lake, your local river, and follow it once round. A cycle explained from no particular place reads as a list.

2. 2

   Write one paragraph per process

   Evaporation, transpiration, condensation, precipitation, infiltration and runoff, collection, and one human consequence. Use the same word for each process every time.

3. 3

   Paste it into openCanviz

   Choose Keep my wording so the narration is the script you checked, set a target length of about three minutes, and pick whiteboard so the diagram builds as each step is described.

4. 4

   Check every arrow and label

   Pause on each scene. Transpiration goes up from leaves, infiltration goes down into soil, clouds are labelled as droplets. Fix any wrong label or arrow in the editor for that one scene.

5. 5

   Watch it muted

   If the drawings alone show the loop in the right order, the video works. If you are handing it in, check your school's rules on AI tools; see /blog/how-to-make-a-video-for-a-school-project.

Common questions

What are the four main stages of the water cycle? At primary level: evaporation, condensation, precipitation and collection. At secondary level you are expected to add transpiration, infiltration, surface runoff and groundwater flow, and often sublimation.

What drives the water cycle? Energy from the Sun drives evaporation, transpiration and sublimation, and the rising air that leads to condensation. Gravity drives precipitation, infiltration, runoff and the flow of rivers and groundwater.

How long does water stay in the air? On average about nine days, according to USGS. Compare that with thousands of years in the deep ocean or in an ice sheet.

What is the difference between infiltration and percolation? Infiltration is water entering the soil surface. Percolation is water moving further down through the soil and rock below. Many school syllabuses use infiltration for both, so match the word your textbook uses.

Does climate change affect the water cycle? Yes. Warmer air can hold more vapour, roughly 7% more for each degree Celsius, which tends to make heavy rainfall heavier and dry spells drier in many regions. For a project on this, cite a named source such as the IPCC with its year.