Although chlorine-free public natural swimming pools have become popular in Europe, so far there has only been one in North America – the Webber Park pool in Minneapolis, which began operations in 2015. That's about to change, however, when the Borden Natural Swimming Pool opens in Edmonton, Alberta later this week. We dropped by to learn more about it.

First of all, how is it even possible for the water in a no-chlorine pool to stay clean? Well, the Borden pool utilizes a system that was created in consultation with three groups – German natural pool company Polyplan, plus the designers of the Webber Park pool, along with Alberta Health Services.

Here's how it works …

When the pool is initially being filled at the start of the season, regular tap water is used. Its chlorine is naturally removed using a filter that contains a mixture of charcoal and shredded coconut shells. The dechlorinated water subsequently flows through a phosphorous absorber (which removes any phosphates present in the water), plus it goes through the pool building's rooftop Neptune filter, which contains crushed granite and live aquatic plants – this helps purify the water by essentially acting as an artificial wetland.

"The sprayers at the top aerate the water, so it gets onto the plants," facility manager Cyndi Schlosser told us, explaining how the Neptune works. "The plants are going to absorb some nutrients out of the water – your phosphates, your nitrogens, and other microscopic components – then the granite filters out other particles, plus the biofilm that grows on the granite will also absorb contaminants."

Once the pool is in use for the year, its water is continuously circulated back through the system, although this time a few extra steps are added.

The water starts by going through a series of three basins that strain out light items such as hairs, while also removing heavier particles, which settle to the bottom. From there, it goes up through the Neptune filter, then through the phosphorous absorber, plus it passes through a system that exposes it to bacteria-killing ultraviolet light.

Finally, before re-entering the pool, the water is heated to a temperature of 23 ºC (73 ºF) – this makes it reasonably comfortable for swimmers, yet cool enough to discourage the growth of bacteria.

So, why bother building a natural swimming pool, when regular chlorinated pools are already tried and trusted? Well, for one thing, natural pools are claimed to be cheaper to run, plus chlorine is irritating to many people. According to facility manager Carveor Triggs, however, there's more to the appeal of Edmonton's new pool.

"The whole concept of returning to a natural pool dates back to the historical origins of Borden Park, where this was actually started as a swimming hole in the early 1900s, and then was first outdoor pool in Edmonton to have heat and enclosed change rooms" he said. "This returns it back to a more natural swimming environment."

The grand opening of the Borden Natural Swimming Pool takes place this Wednesday (July 11th). As with all other outdoor pools throughout the city, admission will be free for the entire summer.

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