We live on a water planet, but lack of water is an increasingly dire concern, contributing to poverty and perhaps even to war.
Most of the world's water is in the form of salt water, which is unsuitable for drinking or agriculture. The majority of what is left is frozen (at least for now). Just one percent of the world's water is fresh, liquid water. Significant portions of this are far from human populations For example, 20 percent in the Amazon Basin, where about 0.1 percent of the world's people live. Where water is near humans, it is often contaminated.
This radio story by Deborah Amos describes a more complicated problem -- in some places the interaction of physical and political geography contributes to water scarcity as upstream and downstream users do not cooperate. Professor Erwin Klaas provides other examples and some maps on his Potential for Water Wars page at Iowa State University. Closer to home, the U.S. is the problematic upstream neighbor along the Colorado River, which does not even reach the Gulf of California most of the time.
With climate change, we can expect such problems to worsen.