Topic 01

The Water Cycle

Earth's water never runs out. It just keeps moving.

Ocean Clouds 1 Evaporation 2 Condensation 3 Precipitation 4 Runoff Groundwater

Almost all of the water on Earth today has been here for billions of years. The water cycle is how it moves between the ocean, the sky and the land.

The five moves

  1. Evaporation. The sun heats oceans, lakes and soil, and water rises as invisible vapor. Plants add more through their leaves (transpiration).
  2. Condensation. Rising air cools and vapor becomes tiny droplets that form clouds.
  3. Precipitation. Heavy droplets fall as rain, snow, sleet or hail.
  4. Runoff and infiltration. Water flows downhill into streams or soaks into the ground.
  5. Storage. Water rests in oceans, ice, lakes, soil and aquifers before moving on.

Where the water is

97%Salty ocean
Mostfresh water is ice or underground
Tinyshare in rivers and lakes

How long water stays put

~9 daysAtmosphere
Weeks–monthsRivers
1000s yrsDeep groundwater, ice

Why it matters

The water cycle sets when rivers flood, when droughts hit, and how much water we have to drink and grow food. As the climate warms, the cycle speeds up: more evaporation, heavier downpours and drier dry spells.