Though fairly common in Europe, "O"natural swimming pools 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.
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,"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.
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.
The water needs to circulate continuously for the plants' roots to cleanse the pool. You also may need to aerate the water so the water organisms' oxygen needs are met. (Without adequate oxygen, your pool could become stagnant, harboring odoriferous anaerobic bacteria.)
Water can be channeled from your pump into your plant zone through the use of PVC tubes. In any climate, bury the tubing in the soil about 18 inches deep. Underwater aeration, which uses less energy than constructed waterfalls and circulates water more effectively, involves diffusing air at the pool's bottom. You can build your own aerator, using an air compressor (1/4-horsepower for a pool smaller than an acre) and high-strength tubing that connects to a diffuser. The diffuser (see "Equipment Sources"), which bubbles air through the water, rests in the deepest part of the pool, where swimmers are not likely to damage it. Connect a brass manifold to the compressor to regulate the air pumped into the pool. I suggests aerating the pool four to eight hours a day: in the morning, when oxygen demand is greatest, and again in the evening. Place your aerator, pump and skimmer in a plastic container, such as a bucket or large plant container, and put a steel-mesh filter mat over the top, to keep debris out of your equipment. Expect to pay $1,000 to $1,200 for a quality underwater aeration system.
Some folks use skimmers hooked up to an additional small pump, to suck off floating undesirables. While these devices are not essential, you might want to consider purchasing one if leaves or seeds from nearby trees and shrubs are likely to litter your pool. The skimmer removes detritus that would otherwise sink and contribute to algae growth.
Installing pumps and compressors can be a tricky business because you're running electrical devices near or in water, You'll want to connect electrical hardware to your home power supply through a buried conduit. Do not run your power through an extension cord. Hire a skilled electrician who will ensure the safety of the system.
Dig you hole and line it with bentonite. Bentonite works as a glue, bonding with the soil particles and preventing pool water from seeping into the ground. Some soils may contain enough clay that simply compacting the pond bottom will enable it to hold water. Talk to local pond builders to find out for sure. But beware: Bentonite doesn't bond well with sandy soil. Particularly sandy soil can require up to 12 pounds of bentonite per square foot, as opposed to 6 pounds in clay-rich soil. Bentonite also can be troublesome when the surrounding soil is very dry. In arid climates, Zingaro recommends bentonite be applied beneath a plastic liner that is woven or textured on the bottom. This liner keeps the bentonite from shifting. In more humid climates, bentonite can be applied directly to the soil. Before treating your pool with bentonite or any other clay powder, thoroughly compact the soil. You can do this with a lawn roller or a plate compactor. Then, while wearing a mask, spread a 2- to 3-inch layer of bentonite powder along the pool sides and bottom. Pack it down with a tractor or plate compactor. Then apply another foot of quality topsoil and compact again.
If you choose a liner, select one made of ethylene propylene diene monomer rather than PVC. EPDM is a synthetic rubber twice as expensive as PVC, but it's worth the extra cost. It has protection from ultraviolet rays, and unlike PVC remains flexible in cold weather. If your soil has a lot of rocks or roots, select a 45- or 60-millimeter liner. You can use a 30-millimeter liner if your soil is very sandy and smooth, and if you and your guests aren't likely to tear holes in a liner while frolicking in the pool. Before laying your liner, compact the sod and cover it with a layer of sand or an absorbent material such as old carpeting or newspaper. Newspaper is a good option: When wet, it bonds to the liner, providing extra protection if the liner develops a small hole.
After the bentonite clay or a liner is installed, cover the bottom of the pool with 4 to 5 inches of gravel. The gravel provides a habitat for beneficial bacteria, which help biodegrade leaves or other natural materials that sink to the bottom of your pool. Make sure you use clean gravel. Fill a 5-gallon bucket with a spigot with some of the gravel you intend to use. Open the spigot and run water through the gravel. If the water comes out dirty, you need to clean the gravel (a taxing, water-wasteful process) or find another source. Expanded shell aggregates and other manufactured gravels are likely to be clean enough to use in your natural pool. In addition to lining the pool with gravel, many people opt to build cobblestone steps for access into and out of the pool. A cantilevered dock built out over the water also provides an easy way to get in and out of the pool, and helps protect the pool's sides. Now fill with water and have a great summer.
Here we are inspecting the tubs, showers for leaks.
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