This Minimalist Public Pool Creates Its Own Water-Filtering Ecosystem

The Borden Park pool in Edmonton, Canada, was designed by Toronto-based gh3* and requires no chemicals to clean its water.

Borden Park natural swimming pool gh3 architecture
The new facility reflects the horizontality of Edmonton’s natural prairie landscape. In fact, the pool sits within the North Saskatchewan River Valley park system, which includes 18,000 acres of parkland that snake through the city. It’s the largest swath of urban parkland in North America. Courtesy gh3*

The water at Borden Park’s new freshwater swimming pool, operating its first full season this summer, is an inviting emerald green. It doesn’t smell like anything—certainly not chlorine. This is Canada’s first public natural swimming pool (NSP)—only the second in North America—and it is kept clean by its own carefully balanced ecosystem.

Though natural swimming pools (NSPs), which use a combination of physical and hydrobotanic filtration systems, are common throughout northern Europe, they have yet to take off in North America. In fact, due to Canada’s strict public swimming pool requirements, the pool is technically considered a “constructed beach.” The site—a public park in Edmonton, the capital city of Alberta—has a long history of swimming; the city’s archives show women in petticoats wading in a pond here in early 19th century photographs. By the turn of the 20th century, the site had been transformed into a simple dugout pool, and by the 1960s, a Modern swimming pool facility had taken its place, complete with chlorine smell. The Borden Park Natural Swimming Pool, designed by the Toronto-based firm gh3* and completed in summer 2018, is its replacement, and a return to nature.

The design of the new building and pool is “an architectural marriage” between the method of water filtration and the project’s context, says Pat Hanson, a founding partner at gh3*. “The project was conceived in a holistic, biophilic way, and the building has a filter as much…as [the] water does.”

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Borden Park natural swimming pool gh3 architecture
Each of the project’s two outdoor filtration pools uses plant life but serves a different function.The hydrobotanic pool uses shade-giving plants like water lilies to provide a sheltered underwater environment where bacteria-eating zooplankton can flourish while the adjacent submersive filter pool uses reed plants to help oxygenate the water. Courtesy gh3*

The rectangular site was organized to separate visitors from two adjacent parking lots: a black limestone gabion wall at the north and a “linear, long, and low” building to the east provide that buffer while framing southern and western views to the park beyond. Visitors enter the facility through doors at the center of the single-story building; from there, they can proceed to universal changing rooms, washrooms, a concession stand, and then continue outside.

The minimalist recreation area is organized around a 8,611-square-foot main pool and a smaller toddler pool, which can together accommodate 400 swimmers at a time. Both pools share beach edges, so they can be waded into without any steps or ladders. To the north, two botanic filtration pools bring a soft texture to the landscape, though these are inaccessible to the public. Sandy areas, aside from serving as beach play areas, also help foster warm microclimates for the cooler ends of Alberta’s summers (the sand absorbs sunlight and radiates warmth during the day). Concrete, accoya wood decking, and stainless steel hardware create a clean finish that offsets the beauty of the green-tinted water. “The pool deck, the sand around the beach, and the accoya wood deck…and the pool gutter [are] all flush,” explains Hanson. “It all speaks to this flatness and expansiveness of the prairie.”

The recreation area also includes six sleek outdoor showers where visitors must rinse off before jumping in, since most chemical sunscreens would damage the microorganisms. That’s because the filtration system, designed in consultation with German engineering firm Polyplan, relies upon the health of its zooplankton, which eat harmful bacteria (and also lend the water its signature color).

Borden Park natural swimming pool gh3 architecture
One side of the pool’s low-slung building is devoted to changing rooms and bathrooms, while its middle section houses spaces for lifeguards and first aid. Its northernmost section includes water filtration and water testing facilities. Courtesy gh3*

This closed loop system is quite nuanced but it essentially works like this: municipal water is dechlorinated offsite before it’s pumped into the pool’s two filtration loops—one for the main pool, the other for the toddlers’. For the main pool, the water is sprayed over a granular filter in the main building. From there, it percolates down roughly eight feet of granite, removing particulates, and is then fed to the pool. For the toddlers’ pool—which is more susceptible to accidents—the water passes directly through the filtration pools outside, which use plant life to clean it. Periodically, water is exchanged between the physical and hydrobotanic systems, allowing each pool to receive the proper balance.

The architects carried the theme of filtration into the language of the building, itself a sort of screen between the serene swimming area and the park beyond. The building’s primary visible material is gabion wall filled with black limestone (sourced from Alberta) that “has synergy with the [granular] pool filtration and is also a common material in the rocky river valley of the Saskatchewan,” as Hanson says. It also allows for air exchange to ventilate the building when it’s not in use: “It’s permeable, so for a seasonal building, it constantly breathes, even through the winter.” Large floor-ceiling doors of weathered steel pivot to open perpendicular to the envelope, also emphasizing flow—whether of people or the elements.

Inside, a limited palette recalls a smart modern cabin. Marine-grade plywood, distressed with black and white stain rubbings, can withstand Alberta’s fluctuating temperatures and humidity, and will take on a greyed patina with time. In the changing rooms, white cantilevered benches accentuate the horizontal.

The project has received the Royal Architectural Institute of Canada Award of Excellence for Innovation in Architecture. Though Borden Park NSP is only in its second season—and its first complete one—it’s easy to imagine other municipalities sitting up and taking notice. Perhaps the tides are changing.

You may also enjoy “4 Innovative Urban Landscape Projects from Around the World”.

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