The Water Cycle

Water: Earth's Most Important Resource#

Water covers about 71% of Earth's surface — but most of it is salty ocean water that living things cannot drink. Only about 3% of Earth's water is fresh water, and most of that is locked in glaciers and ice caps. That makes liquid fresh water incredibly precious!

Where Is Earth's Water?#

• Oceans: 97% of all water (salty)
• Ice caps and glaciers: 2% of all water (frozen fresh water)
• Groundwater: 0.6% (underground, in soil and rock)
• Rivers, lakes, ponds: 0.01% (the liquid fresh water we mostly use)
• Atmosphere: tiny amounts in clouds and vapor

Why Dös Water Keep Moving?#

If the amount of fresh water is so small, how has Earth never run out of it? The answer is the water cycle — a continuous process that moves water from the Earth's surface to the atmosphere and back again, over and over.

The sun provides the energy to power the water cycle. Without the sun, water would not evaporate and the cycle would stop.

The States of Water in the Cycle#

Water moves through the cycle by changing state:

• Liquid water in oceans, lakes, rivers, and rain
• Water vapor (gas) in the atmosphere
• Ice (solid) in glaciers, snow, and ice caps

All three states are part of the water cycle!

Why the Water Cycle Matters#

The water cycle:

• Provides fresh drinking water to all living things
• Fills rivers, lakes, and underground aquifers
• Controls weather and climate
• Cleans water as it filters through soil and rock
• Distributes heat around the planet

Every drop of water you drink has been part of the water cycle for billions of years. The water in your glass may once have floated above dinosaurs!