Less than 1% of Earth’s water supply is ready for human use

The Water Cycle The continuous circulation of Earth’s water supply. Water moves among the oceans, atmosphere, solid Earth and the biosphere The energy source for the water cycle comes from the sun

The Water Cycle WC is balanced meaning that the average annual precipitation over Earth EQUALS the amount of water that evaporates. (What goes up comes down) Evaporation exceeds precipitation over water and precipitation exceeds evaporation over land

Evaporation This step provides clean water for Earth As water evaporates and changes states, it is purified Wind moves evaporated ocean water over land so it can rain over land

Infiltration What happens to precipitation that falls on land? ANS: Some of it soaks into the ground through infiltration Eventually seeps into lakes, streams and the ocean

Runoff The water that Earth cannot absorb flows over the surface of the ground and into lakes and streams. Most runoff evaporates back into the atmosphere Runoff picks up harmful pollutants and carries them into streams and lakes (a bad thing)

Transpiration Plants absorb water from the ground and release it into the atmosphere through evaporation