The water cycle, also known as the hydrologic cycle, is the continuous process by which water is circulated between the Earth and the atmosphere. It involves the movement of water from the Earth's surface to the atmosphere, back to the Earth, and back again.

The water cycle is a closed system, meaning that it is self-sustaining and does not involve the exchange of matter with the environment. It is driven by the sun's energy, which evaporates water from the Earth's surface and rises into the atmosphere, where it condenses into clouds and forms precipitation.

Here's a step-by-step explanation of the water cycle:

1. **Evaporation**: The sun heats up the Earth's surface, causing water on the surface to evaporate into the air as water vapor. This process is called evaporation.
2. **Condensation**: The water vapor rises into the atmosphere, where it cools down and condenses into tiny droplets, forming clouds.
3. **Precipitation**: When the clouds become too heavy with water, they fall back to the Earth as precipitation, such as rain, snow, sleet, or hail.
4. **Runoff**: The precipitation that falls on the Earth's surface flows over the land, picking up any pollutants or contaminants it encounters.
5. **Transpiration**: Plants absorb water from the soil and release it into the air as water vapor through a process called transpiration.
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