Biological swimming pools compared with conventional swimming pools

In recent years, with an increasing awareness for improving the environment, and with a trend of a return to Nature, an increased interest has started to be shown in biological swimming pools and their use as an alternative to the conventional type of pool. A significant turnaround began almost 20 years ago in Europe from where it spread to the United States, Canada and Japan. Now, this concept is gaining pace and is becoming increasingly popular.

A biological swimming pool is an ecological system identical to what is found in fresh water sources in Nature containing plants and organisms of various kinds, all of which have a role to play. Swimming in a biological pool is identical to swimming in fresh water such as lakes, rivers, waterfalls, etc. The main difference between these two types of swimming pools is the way in which the water is filtered and cleaned. In a conventional swimming pool, the water is cleaned using chemicals such as chlorine which has a harmful effect on both of the bathers and the environment. On the other hand, the filtration and cleaning of the water in a biological swimming pool is undertaken in two ways simultaneously. The first is by the vegetation’s roots system and the second is biomechanical filtration using filters whose entire operation is biological. Cleaning and filtering the water is done by the vegetation and microorganisms. The avoidance of using chemicals helps to preserve the environment and safeguard those using the pool, while at the same time offering a swim without any unpleasant smells.

The structure of a biological swimming pool and its environment

A biological swimming pool is made up of three sections. The first is a section rich in vegetation called wetland through which water passes and becomes purified. The second is an area where biomechanical filters are located whose function is to filter and purify the water using microorganisms. In both these areas, both filtration and purification take place. The third area is where the swimmers are. (In an ordinary pool, there is just the swimming area and the filtration machines room only). Apart from purifying the water naturally, the wetland zone of the pool gives added biological value – its design potential. The wetland enriches the landscaping of the swimming pool and makes it more beautiful using vegetation that is a natural part of it. The wetland zone could be a planted area located near to or in the vicinity of the swimming pool. The wetland requires a large area and so, if there is insufficient room near the pool, it is possible, through a correct design, to locate it at a distance of many dozens of meters. The bio-mechanical filters can be positioned in such a way that they need not take up much space. For example, an underground filter room beneath a seating area.

As we have said, a biological swimming pool is an ecological system that contains plants and organisms of various kinds. Fish, microorganisms and the roots of plants are together responsible for how the system works. Fish in the pool have several functions, the most important of which is the removal of mosquito larvae primarily thanks to Gambusia fish. Other fish types are also used that are excellent at eating filament algae, and water beetles that eat toad and frog spawn and microorganisms such as bacteria that also have an important role to play in filtering the water by the roots of plants.

Unlike Europe, where there is less sunshine radiation and more cloudy days, in Israel, the high intensity of the sunlight makes it difficult, at least at the beginning, to obtain the correct balance for the biological system. This is mainly due to the accelerated growth of the algae, primarily the filament type which is liable to constitute a severe problem. By offering the pool some shade, even partially, using trees and/or other elements, less pressure can be put on the system and its efficiency can be increased. Apart from shade, there are other solutions for maintaining the biological system. The solution of shading is best because it does not involve the use of materials that can get into the water and can even reduce the pool’s maintenance work and costs. The ways in which more shade can be provided is by arranging permanent shades that can be dismantled, trees, pergolas and even the shade provided by a building. This is of course provided that the swimming pool design was made together with the design of the house. The desirable amount of shade should be around 40% of the area of the pool. If it has been decided to use trees as a shade solution, then of course there is great importance in choosing the correct type of tree and where to position it in relation to the swimming pool. A tree on the northern side of the swimming pool will not contribute anything. A deciduous tree does have both an advantage and a disadvantage over one that does not shed its leaves, to the point of course, where the selected tree’s root system must be taken into account so that it will not harm the structure of the pool.

Disadvantages of a biological pool vs. a conventional one

Heating the water in a biological swimming pool has the potential of causing damage by the change in the biological balance that had been slowly achieved over the swimming season. Furthermore, it is probable that additional heat would cause an accelerated growth of the algae.

Contrary to a conventional heated swimming pool that can be enclosed completely to maintain the water temperature to permit swimming in the cooler months, a biological pool can only be enclosed partially. Only the area of the pool used for swimming could be enclosed as the wetland section, where the water flow circulates between the swimming pool and the wetland area, cannot be enclosed as it must be open to sunlight. In addition, the water flow that is exposed to the open air necessarily results in a loss of heat. So even if it would be decided to heat a biological swimming pool, a far greater quantity of energy would be required to heat it than would be required in a conventional swimming pool.

Anyone interested in a pool designed with mosaic tiling or a pool with sides colored blue, turquoise or light blue with “starlights” set into the bottom, would be well not to install a biological pool because the accumulation of algae on the sides of the pool is a natural process which colors the pool green and would thus hide all of the decorations that had been so carefully chosen.

To conclude

In designing a biological swimming pool as compared with a conventional one, a complex ecological system must be designed in addition to designing the shape of the pool itself, the finish materials and the water system. Designing an ecological system is not always the same and would probably be different from one location to another depending on the climate, and the microclimate, of that location. Plants and fish that would suit a swimming pool near the coast would not necessarily be suitable for one in the region of Jerusalem or in the Galilee. Each swimming pool must have its own type of vegetation, fish and trees surrounding it. By wisely and correctly creating a design that takes into account all the elements of a biological system, it is possible to create a very luxurious swimming pool that will also give the bathers the additional experience of swimming in Nature.