An alternative to chlorine pools, the BioTop Natural Pools use plants to keep water clean and clear. Wikipedia has some more info on natural swimming pools as well. These could make a great addition to a permaculture design site.
These pools by Master Pools Builders will grab your attention. Imagine sitting in a dry sunken island-lounge area in the pool. See these and more amazing pool features. Article in Luxury Pools Magazine, Spring 2010