Most people have heard Earth referred to as "the water planet." With that name comes the rightful image of a world with plentiful water. In photographs taken from space, we can see that our planet has more water than land. However, of all the water on Earth, more than 99 percent of Earth's water is unusable by humans and many other living things - only about 0.3 percent of our freshwater is found in the surface water of lakes, rivers, and swamps.

The teacher guide describes our current understanding of water cycling and freshwater issues that affect natural and human communities.