A hydrosphere is the total amount of water on a planet. The hydrosphere includes water that is on the surface of the planet, underground, and in the air. A planet's hydrosphere can be liquid, vapor, or ice.
On Earth, liquid water exists on the surface in the form of oceans, lakes and rivers. It also exists below ground—as groundwater, in wells and aquifers. Water vapor is most visible as clouds and fog.
The frozen part of Earth's hydrosphere is made of ice: glaciers, ice caps and icebergs. The frozen part of the hydrosphere has its own name, the cryosphere.
Water moves through the hydrosphere in a cycle. Water collects in clouds, then falls to Earth in the form of rain or snow. This water collects in rivers, lakes and oceans. Then it evaporates into the atmosphere to start the cycle all over again. This is called the water cycle.

Catch a wave, and you're sitting on top of the hydrosphere.
Photograph by Jason Kampf, MyShot
Hydrosphere in Space
Some scientists believe a hydrosphere exists on Europa, a moon of Jupiter, that consists of a frozen outer layer and a giant, liquid ocean underneath it.
cryosphere
Noun
icy part of the Earth's waterincluding icebergs, glaciers, and ice caps.
Noun
our planet, the third from the Sun. The Earth is the only place in the known universe that supports life.
Europa
Noun
moon of Jupiter.
evaporate
Verb
to change from a liquid to a gas or vapor.
Jupiter
Noun
largest planet in the solar system, the fifth planet from the Sun.
liquid
Noun
state of matter with no fixed shape and molecules that remain loosely bound with each other.
snow
Noun
precipitation made of ice crystals.
vapor
Noun
visible liquid suspended in the air, such as fog.
well
Noun
a hole drilled in the Earth to obtain a liquid or gaseous substance.