Natural swimming pools

4th October, 2022 (First published on the old version of this site about 10 years ago. Written by landscape architect, Michael Littlewood, 1933 - 2020)

Introduction

Many people can still remember the joy of bathing and swimming in natural waters in the countryside, whether it was a lake river or a pond, in sunshine or moonlight, whatever the weather, with or without clothes, in groups or as a solitary soul, planned or spontaneous.

However, not all is lost as there are now natural systems for private and public swimming that can be built for the enjoyment of everyone. Natural swimming pools are based on ponds and pools that were once found so abundantly in the landscape.

The comparison to a landscape pool is deliberate because that is what a natural swimming pool is – a large pond with special provision for people to enjoy the water as well as the various creatures that are attracted to it. Nature offers the best examples.

Most pools ponds and lakes are cleaned and purified by the combination of plants and micro-organisms including beneficial bacteria. These micro-organisms break down organic wastes into substances which plants can use directly as nutrients.

The pleasure of using natural water once again for bathing and swimming is now available to many people, whether it is in the privacy of their own home or publicly at a spa, lido, hotel, park, or any recreational centre in the mountains or at the seaside! They are sheer bliss in which to swim and a joy to see.

The Beginning

So how did it all begin? The original concept was developed in Austria by a number of people, who were very conscious of the health benefits of bathing in natural waters found at spas and hydro places. It was not until 1985 that the idea was commercially developed by an Austrian based company, called Biotop, by the founder Peter Petrich. who conceived the idea of a self cleaning biosystem for swimming ponds.Other companies such as Bioteich of Switzerland and Bionova of Germany followed.

How they work

Natural swimming pools, are a chemical free combination of Swimming Zone and aquatic plant garden, known as the Regeneration Zone. Both zones merge together creating an environment that is intertwined and mutually dependent on one another. These ecologically balanced, self cleaning swimming pools combine the natural cleaning properties of plants with filtration and skimming systems so that there is no need for harmful chemicals.

The result is a biologically chemical free clean swimming environment. The water is clear but not sterilised, as in the traditional swimming pool, and it is able to sustain the normal range of pond life, microscopic organisms, invertebrates and even frogs and toads. The aquatic flora and fauna are indicators of the state of the environment and at present their loss in the landscape is huge and very worrying.

The Swimming Zone ranges between 1200 and 2400 mm deep and is plant free. It is usually lined with a rubber liner to prevent water leakage and it is separated from the Regeneration Zone by a barrier wall. This wall prevents the invasion of plants and the substrate and it also makes it much easier to service and drain each zone separately. The wall terminates approximately 250mm below the surface of the pool in order to allow free transfer of water into each zone.

Within the Regeneration Zone the water is cleansed biologically in co-operation with the roots of the aquatic plants and micro-organisms. The aquatic plants act as living filters in this zone and provide an important function in the whole system. These plants absorb decomposing materials and bacteria as well as pollutants from the water and convert them into biomass (organic matter produced by plants and other photosynthetic producers), therefore providing clean water.

Water plants need these nutrients released through the decomposition process for their growth. These nutritional substances, along with E.Coli and other harmful bacteria are then transformed into mineral salts, and are either destroyed or become nutritional elements for the plants.

Zoo plankton is important for the natural swimming pool as they feed on single-celled algae and filter it out of the water. Through this natural self-cleaning process the use of harsh chemicals are not required to keep the pool free from algae and there is very little need for maintenance.

Care

The care and upkeep of the pool can easily be undertaken. The use of a vacuum cleaner for the removal of any silt on the bottom of the swimming zone is an easy task. Likewise the removal of any algae in the springtime and this also presents an opportunity for the owner or children especially to see pool life at a much closer range. The removal of died down vegetation in the autumn is no different from other garden work.

How they are Built

The basic construction requires a deep area of at least 1500 to 2200mm with near vertical walls which need to be constructed for the Swimming Zone and waterproofed by means of a rubber liner with geotextile underliner. The internal walls are constructed from sustainable materials wherever possible such as recycled plastic, stone, timber or geotextile bags. As they will be acting as a retaining structure for the material and plants in the Regeneration Zone, they should be carefully engineered.

The water is drawn down through the substrate in the Regeneration Zone and through perforated pipework to the pump. The water is also taken via the surface skimmer to the pump where it is again filtered before going to the bottom of the Swimming Zone.

The Regeneration zone must be of the same size as the Swimming area and have an average depth of 300mm of substrate, usually graded from 50 to 450mm.

In some pools the plants would surround the Swimming Zone, giving a soft planted margin to the pool. In small pools it is better to plant on one side only so as to avoid a tight enclosed effect. Where space is at a premium, an alternative is to create a second pool, perhaps uphill and allow the water to flow between the bodies of water, probably using a waterfall.

The Regeneration Zone utilises a course inert substrate, such as shingle/gravel and not topsoil or any other growing medium as this would bring high levels of nutrients to the water and would counteract the cleaning effects of the plants., while contributing to the silting process. By planting the aquatic plants in shingle they must draw their nutrients from the water itself and so clean the pool. Also by cutting and removing the plant mass each autumn, the impurities held in the plants are physically removed from the water, allowing the cycle to begin again in the following Spring.

A surface leaf skimmer is also used to help remove floating debris from the water.

Silt, a combination of decaying vegetation, dust and other detritus will always form in any body of water and depending upon the size and location of the pool it can easily be removed by either vacuum or bottom drain system.

A drainage ditch is constructed completely around the pool to ensure that no water runoff enters the pool thereby causing any differences in the pH and the water quality.

Existing swimming pools can easily be converted to the natural process providing that there is space for the Regeneration Zone, either as a separate pool or as a subdivision.

Water Quality

The quality of the water is of special significance. The layout of the pool with its natural Regeneration Zone promotes the self-cleaning forces of the water and the mechanisms provide a long term stable and hygienic quality.. The use of chemicals would only lead to the destruction of the biological balance in the water.

The shallow warmer water of the Regeneration Zone circulates with the cooler deeper water of the Swimming Zone and increases its temperature much more quickly. Solar methods can be used providing care is exercised and it is not used until the plants have grown to combat the algae.

Fish are not allowed in the pool as they cause damage to the water quality and also encourage birds such as herons, as they could also damage the liner. Ducks, geese and any other waterfowl, as well as any pets such as dogs and ponies are also discouraged. As they can contribute pests and diseases.

Planting

The plants are the “engine room” of the whole natural swimming pool and are vital for the correct biological functioning of the system. In addition they also provide habitats for wildlife both in and out of the water as well as an attractive visual scene.

• The use of aquatic plants as a water purifier is a crucial element as they clean the water in the following ways:-

• They provide an excellent habitat for zoo plankton which effectively feed on algae

• They die down in the autumn and winter and when the vegetation is removed any impurities are also taken away.

• They produce oxygen through photosynthesis which is necessary to support all pool life. This assists in keeping the water clear and many plants can have a growth inhibiting effect on the algae.

• Different kinds of plant groupings occupy pools with any streams and bogs thereby creating a distinctive ecological niche for the locality. This local character should if possible be reflected in the overall planting design.

While the technical factors are of the utmost importance there is still the need for consideration of the design principles.

The wide range of aquatic plants provides the designer with considerable opportunities for the creation of a wonderful water garden or landscape.

Wildlife

The natural swimming pool provides an attractive biosphere for various kinds of animals and is quickly inhabited after its creation. They stay mostly in the Regeneration zone that serves them well with food and shelter. There are many predatory insects that feed on mosquito larvae.

Amphibians use the Regeneration zone as a breeding ground too. They appear in early Spring to lay their eggs. However people and frogs do not swim side by side as the amphibians migrate before the swimming season commences.

Health

With the emphasis today on a more holistic lifestyle that incorporates organic food, alternative medicine, spring drinking water, physical exercise, etc then it makes sense to swim in natural water. Numerous users state that the joy of using water free from chemicals is profound.

Chlorine used in conventional pools is a skin irritant and can be associated with rashes like eczema and a number of serious diseases. Chlorine has been documented to aggravate asthma, especially in those children who make frequent use of chlorinated swimming pools. Chlorinated water contains chemical compounds called trihalomethanes which are corcinogens (cancer producing) resulting from the combination of chlorine with organic compounds in water. They do not degrade very well and are stored in the fatty tissues of the body.

Comparisons/Costs

Many people when comparing the cost of a natural swimming pool with a conventional one fail to appreciate the big difference between them. I know from personal experience of having built conventional pools in New Zealand that they are relatively straightforward and easy to build, although the shape and style may differ.

The NSP on the other hand is just the opposite and the client receives not just a swimming pool but a complete water garden or landscape that is beautiful all the year round. In addition, there are no costs for chemicals, maintenance is cheaper and there are huge savings on water as unlike the conventional pools they do not have to be emptied every year. This not only saves money but a scarce resource as well as all the other attributes mentioned above.

Design

There is no doubt in my mind after many years experience of undertaking very large projects in many countries of the world that it is the design that is paramount. While no design can surpass the one created by “nature” the role of the landscape architect is to design in a harmonious and ecological manner ensuring that the impact on the environment is minimal. Start the building process first and the project could destroy the very essence of the place.

Environmental Advantages

• Does not use any chemicals

• Uses less water

• Uses less energy

• Uses materials that are eco-friendly

• Provides a habitat for wildlife

• Less costly to maintain

• Provides educational benefits especially to children

Conclusion

Many users of natural swimming pools have stated “it is that harmony, a seamless blending of environments that is the major advantage”. Many have also said that it has enriched their lives. “While you are separated from the plants you still feel surrounded by them when you swim, which creates a very special kind of mood”.

The colour of the flowers from spring throughout the summer and into the autumn, along with the chorus of the birds and the frogs makes people feel far closer to nature. It provides them with a very special place to be at any time of the day or night, throughout the whole year. It is their very own natural oasis.

All this not only applies to the thousands of private pools that have been built but to the hundreds of public pools in use in Europe for over the last twenty five years. It is very important that the positive attitude to natural bathing and swimming as well as the health giving properties of water, sunshine and gentle breezes on the human body should now be widely recognised both by the leisure industry and governments in the provision of their facilities.

Michael LittlewoodFLI.FSGD. Chartered Landscape Architect (Links to his natural swimming book and his organic gardening book, on Amazon, below).