Water.org provides key basic facts about water issues, especially in developing countries:

http://water.org/learn-about-the-water-crisis/facts/

Anup Shah has come up a comprehensive page about water issues. He touches on many different aspects of water including its environmental, social, and political implications:

http://www.globalissues.org/article/601/water-and-development

Under the “Topics” section of their water page, the Environmental Protection Agency (EPA) of the United States has a comprehensive list of national water issues, often organized by geographic region. While these issues are national issues, most of them are applicable to other regions of the world.

http://www.epa.gov/ow/