I'm glad MR did an entire book focused on the water catchment/filtration system. This book has a lot of examples and shows you the evolution of the process so you really get a good understanding of the basic design ideas behind the systems.
Granted, the text reads like the transcript of a typical Reynolds presentation, and maybe that's what it actually is. But together with the many illustrations, diagrams, floor plans, and photos, this earthship book gives a very thorough overview of probably the most important aspects of earthships: taking care of water needs, including catchment, filtration, and gray- and black water use.