Water Shortages
Rainwater Harvesting for Drylands (Vol. 1): Guiding Principles to Welcome Rain into Your Life And Landscape - Update: One of the best I've ever read. Highly Recommended. Very readable, understandable, and applicable.
Rainwater Harvesting for Drylands (Vol. 2): Water-harvesting Earthworks - Update: Won't be available until January 2008. Volume 3 on cisterns and tanks is even further out. If they are as good as Volume 1, they will be awesome. See http://www.harvestingrainwater.com/
Water Storage: Tanks, Cisterns, Aquifers, and Ponds for Domestic Supply, Fire and Emergency Use--Includes How to Make Ferrocement Water Tanks - Update: Fantastic reference, also a good read, and yet easily implemented.
Rainwater Catchment Systems for Domestic Supply: Design, Construction and Implementation - Update: Another required reference. Lots of background material.
New Addition:
The New Create an Oasis With Greywater: Choosing, Building and Using Greywater Systms - Includes Branched Drains - Art has a way of relating of relaying knowledge to the reader/implementer that is never "Dry", and easily understandable.
We will be discussing the details of this project as we progress at http://groups.yahoo.com/group/rainwater/, and keeping folks up to date here at http://www.green-trust.org as well.
Also see Dew harvesting and Rain Barrels.