Now this is a fascinating idea. Not that it is a new idea since we can assume chemical-byproduct free water existed before we industrialized everything around it. A natural pool is the only way an eco-thinker can do any green swimming without having a beach handy, that is if beaches were waste free… These look very relaxing and I would love to try one out. You can find some truly impressive designs over at Woodhouse Natural Pools. The outdoor ambient sounds on the homepage are quite serene. I am still listening to it as I write.