The water cycle at a glance
The water cycle—also called the hydrologic cycle—is the continuous movement of water around Earth. Water can be liquid, solid ice, or invisible water vapour. It travels through oceans, rivers, soil, living things, and the atmosphere. The cycle has no single starting point; it is a connected system.
1. Evaporation: liquid becomes vapour
Energy from sunlight warms water at the surface of oceans, lakes, rivers, and wet soil. Some liquid water gains enough energy to become water vapour and mix with the air. Evaporation happens at different rates depending on temperature, wind, humidity, and the exposed surface area. Plants also release water vapour through a process called transpiration.
2. Condensation: clouds begin to form
As moist air rises, it often expands and cools. When water vapour cools enough, it condenses onto tiny particles in the air, forming small liquid droplets or ice crystals. Large groups of these droplets or crystals make clouds. A cloud is not water vapour itself; it is made mostly of tiny liquid droplets and/or ice crystals.
3. Precipitation: water returns to Earth
Cloud droplets and ice crystals can grow and combine. When they become heavy enough for the surrounding air conditions, water falls as precipitation. Depending on temperature and other conditions, precipitation may be rain, snow, sleet, or hail. Not every cloud produces precipitation that reaches the ground; some droplets evaporate on the way down.
4. Collection, runoff, and infiltration
After precipitation reaches the surface, some water flows over land into streams and rivers, eventually reaching lakes or oceans. This is called runoff. Some water soaks into the ground through infiltration and may replenish soil moisture or groundwater. Some is taken up by plants, and some can remain stored as snow or ice for a time.
Why the cycle matters
The water cycle helps redistribute fresh water, supports ecosystems and agriculture, and influences weather and climate. The amount of water available in a particular place depends on local rainfall, evaporation, geology, land cover, and how people use water. The cycle moves water, but it does not mean every community has reliable access to clean drinking water.
Follow one imaginary water drop
Imagine a drop in the ocean. Sunlight helps it evaporate and rise as vapour. The air cools, condensation contributes to a cloud, and the drop later falls as rain on land. It may soak into soil, flow into a stream, or be taken up by a plant. Over time it may return to a river or ocean—or follow another route entirely. Real water molecules can take many paths and spend very different amounts of time in each part of the system.
Check your understanding
- What provides much of the energy that drives evaporation?
- How is condensation different from precipitation?
- Name two possible routes water can take after falling on land.
Show suggested answers
- Sunlight warms surface water and helps it evaporate.
- Condensation forms droplets or ice crystals; precipitation is water falling from clouds.
- It can flow as runoff, soak into soil, replenish groundwater, be taken up by plants, or remain as snow or ice.
These are example answers. Other answers may also be correct if they explain the idea clearly.
Key takeaway: Understanding grows when you connect new information to examples and practise explaining it clearly.