Mexico City faces a severe water crisis as 21 million residents slowly drain its aquifer. An environmental group is suggesting a plan to install rainwater harvesting systems on individual homes, but city officials are not convinced it will work.For more global science stories, visit: http://www.world-science.org/NOVA is produced by WGBH in Boston. National corporate funding for NOVA is provided by The Boeing Company. Major funding for NOVA is provided by David H. Koch, the Corporation for Public Broadcasting, and PBS viewers.