Rain, Puddles, and Plants: How Water Travels in Nature

Have you ever watched a puddle disappear after it rains? It doesn't really disappear -- it goes on a journey! The same water that fills your bathtub might have once been part of a cloud, an ocean wave, or even a dinosaur's drink millions of years ago. Water on Earth never gets used up; it just keeps traveling in a big circle called the water cycle.

What happens to a puddle when the sun comes out. How clouds are made and why they turn gray before it rains. The four big steps water takes: evaporation, condensation, precipitation, and collection. Why plants and animals (including you!) need this water journey to keep happening.

When the sun warms up a puddle, tiny invisible bits of water float up into the air. This is called evaporation. You can't see it happening, but it's the same reason a wet sidewalk dries out after a sunny afternoon, or why a wet swimsuit dries on a clothesline. The water didn't vanish -- it turned into an invisible gas called water vapor and floated way up into the sky.

High up in the sky, where the air is cold, that invisible water vapor bumps into tiny bits of dust and turns back into tiny water droplets. Billions of these tiny droplets clump together to form a cloud. This is called condensation. When a cloud gets so full of water droplets that it can't hold any more, the droplets join together into bigger, heavier drops and fall back down as rain -- or, if it's cold enough, snow. This falling water is called precipitation.

When rain falls, it doesn't just disappear either. Some of it soaks into the ground, where plant roots drink it up. Some flows into streams, rivers, and eventually the ocean -- this step is called collection. Then the sun warms that water again, and the whole journey starts over: evaporation, condensation, precipitation, collection, again and again, forever. This is why we say water travels in a cycle -- a cycle means something that repeats in a circle, like the loop on a race track.