Water Cycle

Learn the science of the water cycle

The water you're drinking might have come out of a dinosaur's nose! Before you spit it out you should know water has been everywhere. Water travels. The water you drink could have come from a volcano, then filtered through a giant sequoia tree, ridden the rapids, evaporated into the atmosphere, turned into grapefruit-sized hail, plummeted to the Earth, disappeared into a stream, then circled the world again and again until it ended up in your glass. That's the water cycle.

About 96.5% of the Earth's water is saltwater found in oceans, seas, and bays.
About 96.5% of the Earth's water is saltwater found in oceans, seas, and bays.
Photograph by Galyna Andrushko, Shutterstock

The water cycle is the constant movement and storage of water throughout the Earth. The Earth's water supply never changes. It just travels. The Earth always has 332.5 million cubic miles of water.

In addition to oceans, lakes, and rivers, the Earth stores and transports water in many ways. Water moves through condensation, evaporation, and precipitation (rain and snow). It's stored in ice, snow, and the ground. Even magma contains water—volcanic eruptions bring water from deep in the earth to the surface. The atmosphere also transports and stores water molecules. A water molecule hangs out in the air for about 10 days before condensing and becoming rain, hail, or even morning dew. Then it continues on its trip around the world.

One way water molecules move around is through evaporation from plants. It's called transpiration. Think of it as a plant's version of sweating. Water moves through a plant from the root and eventually evaporates from tiny pores in the leaves. In one year, a large oak tree can transpire 40,000 gallons of water!