Natural swimming ponds are already quite popular in Europe and are gaining interest in the US. Companies like Clear Water Revival (UK) and Total Habitat (US) can help you design your perfect dream pond, or revamp the pool you already have. The cost of new natural ponds versus conventional swimming pools is said to be comparable, but maintenance costs for a chemical-free pool will be much lower. (Just think of the increased health benefits as an added bonus.)
A natural pond is usually larger than a normal pool to accommodate the plants, rocks, and natural vegetation that comprise the filter zone (separate from the designated swimming area). Once water filters through the plant zone, it is then pumped through a UV filter to ensure maximum cleanliness and aeration. Typically, natural ponds have a waterfall to pump water back into the swimming area. Design and shape options are endless.
Whereas a conventional pool is little more than a concrete tub, a natural pond is a landscape centerpiece that will enhance the value of your home and quality of your life. What could be more beautiful than that?
This post via http://www.inhabitat.com/