This single-topic issue of National Geographic magazine highlights the challenges facing our most essential natural resource. “Water: Our Thirsty World” is available for free download starting on World Water Day, March 22, and extending through April 2, 2010. This interactive edition of National Geographic magazine presents complete content from the print edition, plus extra photo galleries, rollover graphics that animate features like maps and time lines, video profiles of photographers who contributed to the issue, and other interactive features. National Geographic’s water issue is available in print on newsstands everywhere beginning March 30.