And Now For Something Completely Different

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Imagine, if you will, your clients this summer lounging by the pool you've just built. What does it look like. Perhaps there's intricate tile work, or beautiful stone decking surrounding the sparkling water. If it were a natural swimming pool, though, you might instead envision your clients sharing the water with a luscious assortment of aquatic plants, perhaps a pebble beach, and even some fish. The natural swimming pool is, in effect, a pond and pool combined. It's quite probable you've never seen one before, as they are not common in the States. AQUA consulted a few experts in the field to find out what they are, how they work and why they're the bees' knees. If you're already a pond builder, you're more than halfway there if you decide to take the plunge into natural swimming pools.

Who Thought Of This?

So how did natural swimming pools come about. "The original idea was developed in Austria by a number of people who were very conscious of the health benefits of bathing in natural waters found at spas," says Michael Littlewood in his article "Natural Swimming Pools," for Building For A Future . Littlewood, owner of British company Ecodesignscape and author of Natural Swimming Pools: Inspiration For Harmony With Nature , goes on to say, "It was not until 1985 that the idea was commercially developed by an Austrian-based company, called Biotop, by the founder Peter Petrich, who conceived of the idea of a self-cleaning biosystem for pools." More than 1,000 natural swimming pools have been built to date in Austria, Germany and Switzerland, according to Littlewood.

Well, What Is It?

Natural swimming pools are defined thusly by Littlewood: "Natural swimming pools are a chemical-free combination of swimming area and aquatic plant garden. The swimming area merges with the planted area, creating an environment that is intertwined and mutually dependent on one another. These ecologically balanced, self-cleaning swimming pools combine the natural cleaning properties of plants with filtration and skimming systems so that there is no need for chemicals or intensive sand filtration."

The total pool area is divided into two vital and distinct zones: the swimming zone and the biological filter, or plant zone. The two zones are separate but equal, literally, and can be either side-by-side or aesthetically separated. The important thing is that the zones are roughly equal, sizewise. Mick Hilleary, author of Natural Swimming Pools and Ponds: The Total Guide and owner of Total Habitat, a design-consulting firm in Bonner Springs, Kan., has built about a dozen pools since in 1997.

"For a solid, medium-sized pool, the swimming zone would be 22-by26 feet, and then the whole thing is more like 40-by-45 feet, because remember the swimming area is inside, like a doughnut hole," he says. "There's an underwater wall holding back the gravel and plants, creating a nice little open zone, and that retaining wall is about 6 to 9 inches below the water level, which keeps the plants and rocks out of the area people will swim in." Hilleary typically constructs this wall out of western red cedar, but other materials also work.

Water garden and pond designer Anthony Archer-Wills often uses fieldstones or boulders as a wall to stop wave action from disturbing the plant zone. "You don't want to stir up the filter medium," he says. "So you need to keep a wave barrier between the swimming and filter area. You would make it look natural because it would be, for all intents and purposes, a loose wall, or possibly a straight barrier for a more formal system."

Along with the wall, there is another key element distinguishing the swimming zone from the plant zone. "There's a dock, or pier. That is very important in that it gives the humans really clean, safe access in and out of the swimming area," says Hilleary. "So they're not trudging through plants and other things to get in and out of the water."

The plant zone is, as mentioned earlier, actually a huge biological filter for waste, but how exactly does it work. "We have a special gravel mix," says Hilleary. "It's special for two reasons. One reason is that it's like lava rock, in that the surface of this gravel has a lot of ins and outs, which increases its surface area. On those surfaces is where our friendly bacteria live. And then we'll draw water by them and they'll eat lunch, which is impurities and things we don't want in the water.

"Another thing the special gravel does, is, we don't want it to contribute to the water quality. If it was normal limestone gravel, the lime would leach out of it and it would run the pH way up in the pond and make an advantage for string algae and other things we don't want. So we use a material called haydite. They put shale gravel in this tumbler that heats up to 2,200 degrees Fahrenheit, and it pops like popcorn and makes this stone that looks a lot like lava rock. But, unlike lava rock, it doesn't leach out anything. It's totally inert. So this haydite gives all the surface area, but doesn't drop lime or minerals or anything we don't want in the water. Underneath the gravel, we've put several runs of slotted drain tile that you might put around your foundation to collect water and then run it off. So what it does, is it sucks water from the pond, it goes over the underwater wall, which is easily accomplished, and then it's sucked down through the plants, down through the haydite, through the slotted drain tile, over to the pump — and this is filtered water, clean water — then it goes through the pump, then it goes through a UV sterilizer. And then the water is pumped back into the pond, usually over waterfalls, down streams and other means of adding oxygen to the water," says Hilleary.

Planting The Filter

Too much plankton algae will turn a beautiful pool into pea soup. The pool ecosystem functions in much the same way as wetlands do, filtering and consuming algae and other organic waste products, and acting as a buffer for the swimming zone in this case. Many different types of aquatic plants are appropriate for the task; what's important is their root system. "You're relying on the plants' fine-hair root system taking the nutrients out of the water and thereby starving the algae by competition," says ArcherWills. "If you had a completely static pond, with no water movement at all, no circulation, you could still achieve clear water, but it wouldn't take the load of fish or humans that you can achieve by forcing the water through the system. You're actually taking the water through the root system, rather than just letting the water slop up against it and hope that the plants are doing their job and are going to seek the nourishment that they need. They're actually being force-fed."

In addition to root systems that trap and consume algae, plants are also chosen for their ability to oxygenate the water. "We use oxygenating plants, and we want to plant it up, so we add things that thrive on the edge, things that thrive in 6 inches of water, and lilies and things like that, that survive in deeper waters," says Hilleary. "Aquatic grasses, dwarf cattails, arrowhead, spearmint have turned out to be fantastic. We mostly recommend hardy, local varieties. But, people do put exotic tropicals in there and they harvest them out and take them into their basement and put a grow light on them in horse troughs and winter them that way."

UV Or Not UV

Though most European builders argue strenuously against use of a UV filter, Hilleary contends that in many areas in the States, it's a necessary backup step to insure that just the right amount of plankton algae lives in the pool to serve as nourishment for the plants. "In [Northern] Europe, they're talking about such cold water that the plankton algae, they don't have much of a population at all to deal with," he says. "So I can understand why they don't want to kill it off. But that's equivalent to Minnesota in the United States. Their system, right out of the box, will not work in Kansas, Oklahoma, Los Angeles, because our water temperatures are so much higher — the biological opportunity is exponentially huge in comparison. So if I kill off 90 percent of the plankton algae, that's great, I have the perfect amount of plankton algae. Because otherwise you get green pea soup, and nobody wants to swim in green pea soup. Also, there's a little critter out there called cryptosporidium. I think the biological filters kill it off just fine, but UV sterilizers will guarantee that. And we size the UV sterilizers for the amount of dosage we need to kill off anything we want to kill off."

How Do You Build It?

"We start digging the hole with certain slopes that aren't too steep," says Hilleary. "It has flat areas where we are going to build an underwater retaining wall, and then it has a deeper part that we make a particular slope." In fact, both Hilleary and ArcherWills said, there is usually no vertical surface at all. After the hole is dug, the liner is placed.

"For the liners, we use one of two," says Hilleary. "First is an EPDM rubber, which is guaranteed for 20 years exposed to UV rays, if you were to use it for a roofing material — and UV rays are about the only thing that attacks this stuff. If when it's 4 feet deep or deeper it's exposed, but otherwise it's covered by rocks and gravel, we expect 30 to 50 years out of that material. Another liner we use where there's a lot of sharp stuff in the soil and we don't want anything poking through the liner, or if it's a very, very big pond, we'll use a fiber-reinforced polyethylene liner, which is also guaranteed for 20 years as a roofing material. The way we put it in, we expect 30 to 50 years out of that."

Usually, there is no other finish applied after the liner is installed. "From the edge down to 4 feet deep, it's all covered with special gravel; you can do pea gravel beaches. I don't recommend sand because it snuffs out oxygen," says Hilleary.

"If you have a lot of sand, a lot of people in it, it will start to kick up anaerobic bacteria and it's just not pleasant. But pea gravel manages to breathe a little bit. You can still lie down on it and walk around on it."

The pool's liner is only exposed from inside the retaining wall, and Hilleary says this has not been an aesthetic detriment. "What's beautiful about it is that it's so black, you get a real nice reflection-pool effect."

After the liner is in place, a pond skimmer and the pump are installed. "Also, we can start building waterfalls and things like that now, and we do liners underneath those things, so that wherever water goes, it ends up safely in the liner."

What's The Difference?

There's a fine line between a manmade pond and a man-made swimming pond. The two main differences are that a natural swimming pool, though constructed of pond materials, is built for a human scale and also that it's filtered much more stringently than a pond alone would be. People must be able to get in and out of the pool easily, says Archer-Wills, if it's truly built for swimming. "Well I guess you can swim in any pond," says Archer-Wills. "I often build a pond, which is also swimable. I would build a deck, or a landing stage out into the deep water, or build a gravel beach so that it's possible to get in and out without disturbing the sediment and silts and the plants. Basically you need an access point where you can get in and out and not muddy the water. Once you're in the water and swimming, you're not going to disturb it at all."

The filtration system also has a much tougher job to do than if there were no people in the pond. "The big difference is the processing power of the whole system, to accommodate the bather load, which has to be dealt with and filtered out," says Hilleary. "You can do a water garden with 1 . 20 of the biological filter we use. We have a lot more of a biological filter and we're moving a lot more water through it than a traditional water garden would require."

Don't Feed The Fish!

A natural setting such as this is bound to attract the attention of inhabitants other than humans. "We recommend that people put fish in, because here's the thing: a natural swimming pool is also a water garden," says Hilleary. "I recommend fantail goldfish and things you can get at the bait store for $4 per dozen. Some people put expensive Koi into these." But, he adds, while feeding them may seem like the right thing to do, owners should resist those impulses. "We recommend not doing that, in fact, more of a problem than having too many fish is people feeding the fish too much. The fish process that food far more and add more of a burden to the filter. After the pond is established, they have natural zones galore to do their own feeding on, and we recommend that."

Minimal Maintenance

People may balk at the idea of taking care of what sounds like two systems — the pool and the plants. But Hilleary contends that maintenance can actually amount to less work than a traditional swimming pool. "A traditional pool often has a perfectly white bottom. So a leaf gets onto the bottom, and you walk up to the edge of the pool and there's a leaf, and you can see it, and 'oh, that's dirty,'" says Hilleary. "A natural swimming pool with a black liner, and all this natural stuff, when a person walks up, there could be 100 leaves down there, and a few stones, and a few fish meandering by, and maybe a turtle. People are so thrilled to see this absolutely crystal clear water, that it's just like they water at the mouth to dive in. So the whole idea of having to net out every single leaf that gets to the bottom of your natural swimming pool is ridiculous. You can let some build up; you can neglect it. We do recommend vacuuming it out in the fall and spring, and we also recommend, if you live around a bunch of trees that lose their leaves in the winter, that you put a net over the whole thing. And there's some really neat, almost totally invisible little nets that you can put over one of these and all the leaves blow off of it, and you can actually still visibly enjoy the whole thing with this practically invisible net on it." But doesn't all that detritus throw off the water balance. "Eventually, if there's too much of it, and that's why we recommend vacuuming twice a year.

Otherwise, everything's been designed with overkill in mind. So we can withstand a little of this and that because there are so many variables out there."

The plants do require pruning after time, but again, the amount is up to the owner. "Some clients neglect it totally and they hire us to come in twice a year and clean things up. And then I have other clients who are totally involved and planning new plants, and really take a hobby-like involvement in the pond," says Hilleary.

Jump In

Ready to give natural swimming pools a try? "Pond builders are 90 percent there," says Hilleary. "Now, swimming pool builders need to go to pond building school, and then they're 90 percent there." Hilleary says it takes about a month to build a natural swimming pool. "If you're going to hire me to do it, turnkey, it's going to be $30,000 to $40,000, probably, for a good medium-sized pool. So it is true that these are about the same cost as an in-ground pool, but because they're so natural, they beg for additional natural elements like waterfalls and rock geology and stuff like that, which add to the cost."

Natural swimming pools will certainly never usurp the traditional ones for backyard recreation, but they do provide a beautiful alternative, and one that allows owners to feel more connected to their surroundings. Says Archer-Wills, "One just looks at nature and sees streams with water trickling through the gravel beds and the plants, and they're invariably clear, except after a heavy rainstorm. So it's not rocket science, or anything remarkable at all, it's just working with nature, and encouraging nature to do the job for you."

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