No chemicals, plenty of cattails. That's the premise of a new concept for pools, described in detail in this backyard pool New York Times piece. Here's an excerpt:
"The “natural pools” that Total Habitat builds are bordered with wood, planted with lush vegetation and free of chemicals like chlorine; they resemble nothing so much as a swimming hole. “It’s natural-looking, like a pond,” Mr. Hilleary said. “But the water looks so clean. People really want to swim in it, more than in a farm pond.”
Natural swimming pools (or swimming ponds, as they are called in Europe, where the concept originated 20 years ago) are self-cleaning pools that combine swimming areas and water gardens. Materials and designs vary — the pools can be lined with rubber or reinforced polyethylene, as in the case of Total Habitat’s, and may look rustic or modern — but all natural pools rely on “regeneration” zones, areas given over to aquatic plants that act as organic cleansers."