# Natural pool

A natural swimming pool or natural swimming pond (NSP) is a system consisting of a constructed body of water, where the water is contained by an isolating membrane or membranes, in which no chemicals or devices that disinfect or sterilize water are used, and all clarifying and purifying of the water is achieved through biological filters and plants rooted hydroponically in the system.
This definition is based on the FLL (Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V - the Landscaping and Landscape Development Research Society) publication "Recommendations for the planning, construction and maintenance of private swimming and natural pools" 2006 Edition.
It is called a "natural swimming pool" because the filtration systems used have biological equivalents in the natural world. In fact if there is not an example of the type of filtration being used in the natural world then it is not seen by the IOB (International Organization for natural Bathing waters) to be naturally filtered. Natural aquarium and koi ponds also exist, but use algae scrubbers for their filtration.
Systems that use UV, ozone and copper/silver ion disinfection techniques are examples of non natural methods and, by definition, are not Natural Swimming Pools.

## History

The first NSPs were built in the early 1980s in Austria, where they are known as Schwimmteiche. The first was built by DI Werner Gamerith in his private garden. Some of the first companies to use the idea of NSPs commercially were the Austrian firm, Biotop Landschaftsgestaltung, and the German firm, BioNova. In 1990 the first public NSP was built by BioNova, followed by another one in 1991 built by Biotop in Unzmarkt (Styria, Austria)
The market for NSPs spread into Germany in the late 1980s. In 1998, the first public NSP in Germany was designed and built by Gerhard Brandlmeier and Rainer Grafinger of BioNova.
The residential market for NSPs spread throughout Europe into Switzerland, the United Kingdom, France, Italy, Spain, Belgium, Holland, Hungary, and the Czech Republic. In 2002 Total Habitat founders Mick Hilleary and Dale Gracy published the first English language book on Natural Swimming Pools.
The American market was introduced to natural swimming pools when The New York Times published an article. The article states-incorrectly-that "all natural swimming pools rely on regeneration zones, areas given over to aquatic plants that act as organic cleansers. This false statement is proven untrue by the work of Mr. Hilleary and his team. Natural Swimming Pools do not need to have regeneration zones. Although this is the most popular method in the European market, Natural Swimming Pools may also use beneficial bacteria as a means of filtration. This allows for smaller overall areas and for swimming in all parts of the Natural Swimming Pool.
Today, there are over 20,000 NSPs in Europe, 100 of which are actually public pools in Germany. Bad Maria Einsiedel, designed by BioNova, marked the 100th public swimming pool and was opened to the public in Munich on June 7, 2008. In the Summer of 2010 the first public natural pool in Sweden was built by BioNova in the city of Sigtuna. In July 2011 the first Indoor Natural Swimming Pool was built by Clear Water Revival in Cornwall, UK.
The first public natural swimming pool in North America was finished at Webber Park in Minneapolis in 2015. The Minneapolis Park and Recreation Board hired the Landform Group and BioNova to provide all of the technical planning and construction details for the project. The outdoor pool includes over 20,000 square feet of swimming area along with 16,000 square feet of planted regeneration zone, and it has been designed to accommodate over 1,000 bathers per day.

## Cleaning, sanitation, and water quality

NSPs rely on a combination of hydraulic design techniques in conjunction with a finefilter. Materials such as leaves, pollen, dust or suntan lotion commonly found floating on the water's surface are removed by a specialized skimmer or overflow channel. These specially designed devices allow optimal skimming of the water surface and reduce silting. Downstream, a bioreactive biological filter removes and retains additional particulate matter down to a particle size of 100 micrometres. Pumps different from those found in conventional pools hydraulically optimize water flow rates and volumes, thereby accelerating the cleaning process even further. This mechanically enhanced natural filtration produces clear, clean water. In fact, when NSPs are installed in Europe, pool owners and builders will ceremoniously wrap up an installation with a ceremonial drink of water collected directly from the pool.
A biofermenta system is the latest form of filtration for NSPs reducing the need for large plantation areas and filtration beds.

### Health standards

European and European-style NSP builders follow the EEC bath waters guideline 2006/7/EG concerning the quality of bath waters and their management. Specific health guidelines are also clearly established in the German FLL Guidelines, which are adhered to by NSP builders throughout Europe. On March 4, 2006, new pool water standards were published in the Official Journal of the European Union. These standards, enacted throughout Europe within two years, outline the methods of monitoring pool water quality. Unlike conventional North American swimming pools whose sanitation levels are monitored by testing for proper pool chemical balance, European-style NSPs maintain strict standards for bacterial levels. Peter Petrich, an originator of natural swimming pools in Austria, has said that the risk of swimmers becoming sick is "very low."
Properly built public NSPs in Europe, some that see up to 3,000 swimmers per day, are able to meet these high sanitation standards. The first public Natural Swimming Pool in North America has been designed to accommodate over 1,000 bathers per day. Thus, the efficacy of the NSP cleaning process remains in little doubt, even though no guidelines for natural pool water quality currently exist in the United States.

### Temperature and feel

Although certain undesirable microorganisms are able to survive at sustained temperatures over 82 °F (28 °C), below this temperature these harmful bacteria are completely out competed by the natural filtering bacteria in certain types of natural swimming pools.
Earth-friendly heat pumps and solar panel warming systems can be incorporated into NSP construction to keep with the eco friendly feel of a natural pool however normal electric or gas heaters work just as well.
The water in NSPs has many desirable characteristics. For example, the red eyes, dried out skin and hair, and bleached bathing suits associated with overly chlorinated water are not issues with NSPs.

## Care and maintenance

Each NSP is unique so each has a different "break-in" period during which the system finds balance. While NSPs can be used for swimming immediately, it takes approximately two to three years until a stable biological equilibrium is reached. Once an NSP has reached equilibrium, it requires considerably less regular maintenance than a conventional swimming pool. Seasonal care and maintenance is still required over the course of the year, though even this differs from care of a conventional swimming pool. For example, ducks and other water fowl in migration have been known to visit NSPs during the winter months.

### Spring

As winter turns to spring, plants in the regeneration zone must be pruned and tended to avoid over growth, just as in any typical garden. Any dried or dead plants must also be removed.
Migratory water fowl also tend to stop at natural swimming ponds in the late winter and early spring months. While they may add to the bucolic aesthetic of a well-built NSP, steps must be taken to minimize any foreign contaminants that would compromise swim water quality that such animals can introduce to the NSP (e.g. installing filtering plants such as water hyacinth and water lettuce).

### Summer

On windy, warm, and dry days, water can evaporate at the rate of up to 1 cm per day. If the water level gets too low, water must be refilled in order to protect the plants planted hydroponically in the regeneration zone.

### Autumn

Dead leaves that fall off trees can make their way into the pool and decompose, introducing microorganisms and nutrients that may serve as food for algae growth. In the late autumn months, netting can be stretched over the pool to catch larger leaves before they fall into the NSP.

### Winter

While NSPs are allowed to freeze over, and many owners enjoy seeing frozen ponds in their backyards, extended freezes should be avoided as carbon dioxide can accumulate underwater, unbalancing the NSP system. Excessive snow cover may also damage the plants in the regeneration zone.

## Ocean pools

In the early 20th century, especially in Australia, ocean pools were built, typically on headlands by enclosing part of the rock shelf, with water circulated through the pools by flooding from tidal tanks or by regular flooding over the side of the pools at high tide. This continued a pre-European tradition of bathing in rockpools with many of the current sites being expanded from sites used by Aboriginal Australians or early European settlers. Bathing in these pools provided security against both rough surf and sea life. There were often separate pools for women and men, or the pool was open to the sexes at different times with a break for bathers to climb in without fear of observation by the other sex. These were the forerunners of modern "Olympic" pools. A variation was the later development of sea- or harbour-side pools that circulated sea water using pumps. A pool of this type was the training ground for Australian Olympian Dawn Fraser.
There are currently about 100 ocean baths in New South Wales, which can range from small pools roughly 25 metres long and "Olympic Sized" (50m) to the very large, such as the 50 × 100 m baths in Newcastle. While most are free, a number charge fees, such as the Bondi Icebergs Club pool at Bondi Beach. Despite the development of chlorinated and heated pools, ocean baths remain a popular form of recreation in New South Wales.
A semi-natural ocean pool exists on the central coast of New South Wales; it is called The Bogey Hole.