By Alan Weene

Natural swimming pools (NSPs) are chemical-free, ecologically harmonious, and safe for humans and the environment. Rather than via the use of chemicals, pool water is mechanically purified by beneficial microbes and carefully selected aquatic plants as it is mechanically circulated through botanical and biological filters. The result is a biologically active, living system that can create clear, clean, and safe water for swimming.

A Brief History

Constructed wetlands technology for swimming pools originated in Austria more than 30 years ago. The first Schwimmteich (swim pond) was built in 1983 by Werner Gamerith and was designed as a single contained vessel using no pumps or filters. Today, NSPs have evolved into fully customizable single- and multi-chamber vessels incorporating principles of limnology, hydraulics, and modern pool construction techniques. Controlled directed flow through skimmers, filters, and a planted wetlands area (i.e. regeneration zone) can provide optimal water quality and clarity. Popular in Europe, this technology is now available in Canada and the United States and is rapidly gaining popularity.

What is an NSP?

By definition, a natural swimming pool is a contained, closed-loop system in which no disinfectants or devices are used to sterilize the water. This means no UV, no ozone, no copper or silver ionizers, and no chlorine. The living water is mechanically circulated between a plant-free swimming area and the regeneration zone, where aquatic plants are hydroponically rooted. In a single-chamber design, these two areas are physically separated by a submerged retaining wall, while in a multi-chamber design, the swimming area and regeneration zone can be adjacent to each other or completely separated by the landscape.

A general rule of thumb is that the swimming zone’s surface area is approximately equal in size to the regeneration zone, although the total footprint varies depending on the NSP’s style. For example, a multi-chamber natural swimming pool can have a regeneration zone that is as small as 30 per cent of the total footprint, while a single-chamber NSP is typically 50 per cent. If space is a concern, part of the regeneration zone can actually be concealed under a deck or even beneath the lawn, where water circulates through a contained chamber. These areas are dry at the surface and can be walked upon.

The aquatic plants in the regeneration zone create a colourful waterscape throughout the swimming season. These plants perform the function of nutrient extraction, effectively out-competing algae and other micro-organisms for available resources. An assortment of native and adapted marginal, floating, and underwater plant species are used. Common examples include cattails, American lotus, pickerel weed, and several varieties of flowering water lilies. Many of the plants selected for NSPs are hardy perennials that will come back in the spring just as they would in natural bodies of water, such as ponds or lakes. Some replanting of perennials and flowering annuals is typically necessary at the beginning of the growing season. While natural swimming pools are suitable for all normally habitable climates, plants are selected based on climate hardiness. As with traditional swimming pools, the pool vessel is structurally engineered to prevent freeze damage. In regions experiencing subfreezing temperatures, an NSP does not need to be covered in the winter and can be used for ice skating.