Designing a biopool: 100% eco-friendly and chlorine-free

What it is, how it works and guidelines for making one

Inspirations / How to

26/06/2023

Estimated reading time 6 minutes

A biopool is an artificial body of water separated from the ground by an impermeable layer and designed for diving, swimming etc. It is therefore a natural artificial pool, halfway between a lake (a natural basin) and a traditional pool (custom-built). Its peculiar characteristic is that rather than using chemical substances to disinfect the water, it is purified using natural processes, in which aquatic plants play a major role. It is therefore a small, living ecosystem that filters and purifies the water by itself.

Biopools are also known as natural pools, biolakes or swimming ponds. Generally speaking, it is more accurate to define a biopool as a natural pool, where the water is purified in a separate area from the area where you bathe, and which may look similar to a traditional pool (same geometric shape, presence of elements such as access steps, solarium and so on).

In any case, it is the physical, chemical and biological processes that regenerate the water, making it hygienically suitable for bathing, that differentiate a natural pool. It is not characterised by any particular construction method, nor does it have a certain shape (geometric or free-form). The phytodepuration processes are the same as those found in nature, for example in lakes or marshy areas. The result is not an "aseptic" environment like that of a conventional swimming pool, but a natural one with clean, transparent water, and without the pungent odour of chlorine or irritation to the skin, eyes and respiratory tract. This natural characteristic is also prominent in the colours that typically characterise biopools: not pure whites and artificial blues, but the greens and browns found in many wild aquatic environments.

In this article we will look at how to design a DIY biopool and what guidelines you should follow to build it to a high standard.

How a biopool is made

The basic components of a natural pool are a bathing area, phytodepuration area and systems that facilitate its operation. The first is a free-form area filled with water, intended for swimming and relaxation. The second is used to regenerate the "used" water from the bathing area, with help from aquatic plants. Based on your tastes and budget for your DIY biopool, you can achieve different degrees of integration between nature and technology, for example to facilitate maintenance or maximise purification potential: from no-tech solutions to an extensive array of technical systems, and various combinations of both. The hydraulic system can include filters and pumps, preferably energy-efficient ones, for recirculating water from the phytodepuration area to the bathing area, or to force it through the phytodepuration area itself. An electrical system is needed to operate filters, pumps, lights (if any) and so on.

A natural swimming pool does not use chemical products or treatments (such as chlorine and its derivatives), nor UV rays or other means to disinfect the water, unlike conventional swimming pools. Instead it uses phytodepuration, a process that exploits the synergy between aquatic plants, the substrate in which they anchor their roots (gravel or other inert material) and a host of microorganisms (various types of plankton and "good" bacteria). It is an effective system designed to purify highly polluted water of domestic and industrial waste. While the microorganisms live by breaking down the pollutants into compounds that become nutrients for plants, the plants provide the microorganisms with oxygen through photosynthesis, as well as a habitat among the roots. The aquatic plants also compete with algae for nutrients, thus keeping the algae in check. In addition, the competition with the microorganisms, the effects of the sun's rays and the temperature deactivate pathogens ("bad" bacteria, fungi, etc.).

How to build a natural swimming pool in the garden

A natural pool is a living ecosystem that needs time to reach an ecological balance. Just how long this takes depends on the individual pool and can be determined by meticulous research. Take all the time you need to prepare and build your DIY biopool project, or entrust the job to landscaping professionals and a specialised construction company.

Your design of your natural swimming pool must take into account you and your family's lifestyle, as well as the characteristics of your house and garden. It must also consider a series of factors, such as the local climate, sun exposure, terrain (flat or sloping), existing vegetation (large roots can damage the waterproof coating or the structure of the biopool, whereas foliage that provides too much shade and leaves falling into the water will affect its ecological balance). Pay attention to safety, especially if the biopool will be used by children: provide a nonslip entry point into the water, a perimeter fence all around and other safety features.

After designing the pool, you need to excavate the area at the depths determined for the bathing and phytodepuration tanks (a digger will be needed to move the earth). If the soil is stable (clay-rich or medium textured), you can directly cover the excavation with a sturdy geotextile and overlay it with waterproof sheeting (made of EPDM, FPO or PVC). In the phytodepuration basin, before filling the bottom with gravel, lapilli or zeolites to form the bed of inert material that serves as a substrate for aquatic plants, lay another protective geotextile. At this point, it is time to install the technical systems. A transporter will expedite the work on site by transporting materials, equipment, plants and everything you need to build your do-it-yourself biopool.

In a natural swimming pool, aquatic plants don't just serve an aesthetic function but, as we said, also act as an organic filter. There are different types: submerged plants, semi-submerged plants (particularly water lilies and lotus flowers), marsh and shore plants. Each type performs one or more roles: providing shade, oxygenation, providing a habitat for the phytodepuration microorganisms, etc. Choose and combine the aquatic species by evaluating the climate, life cycle in the seasons, the correct depth for planting them, the water characteristics, possible interactions (some plants are invasive), ease of management and so on.

The edges of your DIY biopool should be finished according to its shape and immediate surroundings. You can use stone, wood, brick, or living materials such as grass or low shrubs. In the latter case, allocate some extra time to collect clippings, leaves and flowers so that they don't end up or remain in the water and thereby upset its equilibrium. In addition, when trimming the grass with a brushcutter or lawnmower, be careful not to cut the waterproof sheet of your natural pool.

 

A convenient solution for the lawn could be to lay rolls of turf (in the linked article you will find instructions for doing just that). Alternatively, you can use a rotary tiller to prepare the soil before planting shrubs along the edge of the biopool, or a hedge to serve as a fence. On the subject of evergreen hedges, here's how to choose one, plant it and prune it.

 

When filling your natural pool you can use water from the mains supply, a well or even rainwater. Make sure there are no local water conservation regulations that restrict the use of potable water. If, on the other hand, you are not using drinking water, check by means of a laboratory analysis that its quality is suitable for bathing. In fact, once it is purified, rainwater is an excellent resource that can be exploited for free—for example using a collection system and a water pump—to fill your DIY biopool and top up the level, which will fall due to evaporation (by the way, bear in mind that natural pools are neither covered nor emptied in winter).

Biopools: permits, red tape and other considerations

Are permits required for biopools? In general for private pools that are not open to the public (like that in your home garden) there are no obligations to be complied with as regards water sanitation. There also shouldn’t be any regulations regarding the technical and construction characteristics, but it is worth checking whether there are any specific planning restrictions.

If the design of the natural swimming pool for your garden includes building-type structures (such as a reinforced concrete basin), you may need to apply for planning permission or submit a Commencement Notice to the building control authorities. It all depends on the size of the pool compared with your home, as well as any planning constraints. We advise you to clear up any doubts by enquiring with your local council. This does not apply to public and private biopools for public use (such as a biopool attached to a farm stay).

A biopool is not only a cross between a swimming pool and a natural lake, but it also resembles the ornamental ponds of gardens where water is an integral feature, such as in Japanese and English-style gardens. Here you will find several ideas for designing an English-style garden.

Are you worried that your natural pool will attract mosquitoes to your garden? These annoying insects love standing water, whereas the water in biopools is always moving and attracts their natural enemies, including dragonflies. Nevertheless, here are our tips for getting rid of mosquitoes in the garden.

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