We are currently working on several projects which include swimming pools. In most situations our clients request covered and heated pools which are kept clean by adding chemicals. The downside of this is that chlorine is not particularly kind to our skin or the environment and quite often the pool has to be covered for the 355 days when the weather is too cold to swim. One of the joys of UK life!
The sustainable alternative is a bio-pool which has an outer margin of aquatic planting which filters the water leaving an open and natural 'swim-zone'. The pool attracts wildlife, is cheaper to maintain and of course, adds to the overall visual appearance of the garden. Note: It's no warmer :-)