Though fairly common in Europe, natural swimming pools (like the one pictured above in an Austrian family's backyard), are in their infancy in the United States. Ask most American swimming-pool contractors to build a backyard pool and chances are they'll roll out a long list of goods, including rebar, gunite, fiberglass, chlorine and an energy-sapping filtration system. But in recent years, a few builders and a growing number of homeowners have learned how to build pools without relying on a mass of manufactured materials and chemical additives. They've found it's possible to construct pools that are more about building with nature and blending into the natural landscape. Natural swimming pools use gravel stone and clay in place of concrete or fiberglass, and aquatic plants instead of harmful chemicals and complicated mechanical filtering systems. The plants enrich the pool with oxygen, support beneficial bacteria that consume debris and potentially harmful organisms, and give habitat to frogs, dragonflies and other water life. The result is a beautiful, ecologically diverse system that is relatively inexpensive to construct. (A natural pool can he constructed for as little as $2,000 if you do it yourself, while conventional pools can cost tens of thousands of dollars.) Natural swimming pools require no harmful chemIcals, are fairly low-tech, and once established call for only a modicum of management. You won't have to drain the pool each autumn. Except for topping it off now and then, you'll fill the pool only once.
DIG IT
The cheapest and most ecologically sound way to build a swimming pool is simply to hollow a hole in the ground. You can make your pool as shallow or as deep as you want, but the key is to make sure the sides slope: Otherwise the soil will cave in. The ratio should be a 1-foot vertical drop for every 3 horizontal feet. "It's not a bathtub effect, but more like a soup bowl," says Tom Zingaro, partner with Denver-based Blue Lotus Designs, a pool-and pond-architecture company. One of the main reasons traditional swimming pools are constructed with a steel framework is to ensure the walls stay vertical and perpendicular to the bottom surface of the pool. Construct a pool with sloping sides and you'll eliminate the need for any steel reinforcement.
ZONING
Reserving at least 50 percent of your pool's surface area for shallow plants, either at one end or in a ring around the sides, eliminates the need for chlorine and expensive filters and pumps. You'll want to separate the swimming area of your pool and the filtration area, or plant zone (see the illustration). A rim within an inch of the water's surface keeps plants in their place but allows water from the swimming area to move to the plant zone for filtering, As water passes through the fibrous root structure of the plants, bacteria concentrated on the plants' roots act as a biological filter, removing contaminants and excess nutrients in the water. Decomposer organisms, also found in the plants' root zones, consume the bacteria, effectively eliminating underwater waste buildup.
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