This is the beginning of the research for water retention.
Rain Garden - A rain garden is a planted depression that allows rainwater runoff from impervious urban areas like roofs, driveways, walkways, parking lots, and compacted lawn areas the opportunity to be absorbed
Ozy Wastewater system - interesting how they actually use the waste water to flush. Also interesting to see how much more water the shower and bath use than anything else. Making use of an outside bath / shower as i've been wanting to do for while and then re-using that water could be a good idea.
Reduce your lawn - Turfgrass is one of the most water and labor-intensive types of "gardens" you can have. Consider planting groundcovers or low-maintenance perennials instead.
Graywater - a comprehensive resource about greywater planning. It seems very modern but in the end is selling a drip tube system. But lots of good info.
Create an Oasis with Greywater - by art ludwig. He's supopsed to be one of the authorities on this stuff
Rainwater harvesting for drylands (vol 1) (vol 2) - by brad lancaster - again he's supposed to be an authority on this stuff.
http://www.harvestingrainwater.com/ - Brad Lancasters site
http://oasisdesign.net/ - art ludwigs site