Nestled between vineyards and the lush hills of Switzerland, a new sustainable outdoor pool is making a splash—just in time for summer. It has been nearly 35 years since Herzog & de Meuron first won the commission to replace the outdated baths by the banks of the River Wiese with a new public pool in the town of Riehen. And now, decades later, residents can plunge into Naturbad Riehen, the town’s new chlorine-free, lake-inspired bathing facility, to cool off from the heat. The pool, a modern take on the traditional wooden baths along the Rhine, officially opened in late June. For visitors, the new building offers several amenities, including a café, showers, storage spaces, and a water pump station.
“The water feels very different from the usual chlorine processed pool; chlorine dries the skin, irritates eyes, and has a strong smell,” says Michael Bär, an associate and project manager at Herzog & de Meuron. “In the history of sanitation in industrial societies it can be seen as a necessary compromise to keep water clean, but if you have the possibility to swim in natural clean water this is a better option.”
The exterior of the facility, including the deck, docks, and roof, are made of wood. The firm selected larch for the construction and façade and rough timber for the outer perimeters. To reduce energy consumption, all the wood was processed in Switzerland. The pool steps are made of smooth concrete rims filled with round, barefoot-friendly gravel.
Fashioned after a natural terrestrian water purification system, the pool is split into two areas: one for swimming and a regeneration section for water treatment. In the latter area, the “used water is passed through an area planted with aquatic plants and bulk soil,” says Bär. “Here germs are eliminated by mico-organisms and plants that absorb the nutrients in the water for their growth.” Skimmers, like in chlorinated pools, are used to help capture and remove particles and debris. The water treatment and purification uses biological filter terraces without chemical additives. Sensors responds to any changes in water quality-- if for instance, rainwater overflows into the drainage system-- by increasing the pumping into the filters.
Herzog & de Meuron plans to eventually use a filter with specialized plants to naturally remove phosphates, coliform bacteria and bio particles.
Photo © Leonardo Finotti