EXPLORE: Earth's Water (BrainPop)
1. READ: Where is Water Found?
Earth's hydrosphere is composed of many reservoirs, places where water is stored. Water is an overlapping component of each of earth's spheres - the biosphere, geosphere, and atmosphere all contain water. Earth's water is stored in clouds, oceans, ice caps & glaciers, lakes, rivers, living organisms, soil, and as groundwater.
The largest of earth's reservoirs is the ocean. In fact, 97% of all the water on our planet can be found in the oceans. Only 3% of our planet's water is freshwater - water that can be used by living things. Most of the planet's freshwater is trapped in glaciers, ice caps, or underground aquifers. Only a small amount of freshwater is found on Earth's surface as lakes and rivers, yet this is the source for most of the water people use every day.
How long a molecule of water will stay in one of these reservoirs is known as its residence time. Water will stay in some reservoirs for a long period of time; for example, groundwater and ice sheets typically have long residence times. Water does not typically spend a long time in the atmosphere before it condenses and falls back to the earth as precipitation, so this particular reservoir has a short residence time. Soil also has a short residence time because water is readily lost to evaporation or easily seeps into the ground.