I know that some of the skoolienuts here have expressed interest in rainwater harvesting to extend water use. I downloaded a free ebook (pdf) called The Texas Manual on Rainwater Harvesting
(caution the link will immediately download the pdf) and it gives a good amount of info as well as diagrams that show how to build a First Flush Diverter.
Texas A&M AgriLife Extension Service's Rainwater Harvesting
website is a good source of more info (but their books aren't free). You can read short descriptions of various ways stored rainwater is used. At the end of each use is a section where additional material (books) that addresses the specific use is recommended.
Downloading the free Manual and reading the website is a good start if you are interested in constructing a rainwater harvesting system. The manual addresses harvesting rainwater for potable use as well.
Edit: fixed link again on 8/8/2014.