National Geographic's recently released April 2010 issue "Water: Our Thirsty World" is a single-topic issue that focuses on the challenges facing our most vital resource: water. The articles focus on water related issues from pollution to scarcity to water infrastructure management while covering everything in between.  In addition to well researched and written stories on water, the issue also features impressive water pictures, maps of the world's water resources and informative graphics on water. The 184 page issue is available for free online until April 2 here. After April 2, it will only be available in its print version at a news stand or by subscription.