water cycle
The water cycle is the journey that water takes around our planet, over and over, with no real beginning or end. The Sun heats the ocean and warms puddles until water rises invisibly into the air as vapor (evaporation); high up where it's cold, that vapor gathers into clouds (condensation); the clouds let go as rain or snow (precipitation); and the water trickles downhill through rivers and soil, back to the sea (runoff), ready to climb skyward again. So the Sun lifts water up and gravity pulls it back down, turning the loop together. Hang wet laundry in the sun and watch it dry — you've just witnessed the first step.
This endless loop is why we have fresh water at all. The ocean holds almost all of Earth's water, but it's salty; evaporation leaves the salt behind, and the water that falls back as rain and snow is what replenishes the fresh water we can drink. Every river, lake, glacier, and raindrop is borrowed from this cycle, and the same molecules have been recycled for billions of years.
A common misconception is that the cycle creates or uses up water. It doesn't — the total amount on Earth barely changes; the cycle just keeps moving the same water between sea, sky, and land. So the water in your glass today may once have fallen as snow on a dinosaur.
evaporation → condensation → precipitation → runoff → (back to evaporation)
The four main stages, looping endlessly — driven by sunlight and gravity.
Also called the hydrologic cycle, from the Greek hydro, "water." Plants play a quiet part too: they pull water up through their roots and breathe it out from their leaves — a step called transpiration that, in a forest, can lift as much moisture skyward as a lake would.