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

2. 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

3. 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

5. 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

6. 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

7. 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)

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