How to build a natural pool
The natural pool or swimming pond is the new frontier of ecological bathing. In this tutorial we take a look at how to build a natural pool.
Today, more and more environmentally conscious people are looking for an alternative to the classic swimming pool with blue tiles and chlorine-smelling water.
The natural alternative to the swimming pool is the natural pool or swimming pond!
In conventional swimming pools chlorine is used as a disinfectant, but it creates serious problems for those who swim in the pool, as it alters the pH of the skin and damages the hair, eyes and respiratory system. And not only that, some scientific studies are also analysing an increased risk of certain forms of cancer.
In the meantime, natural pools, in which water is purified by aquatic plants, without the need of chemical additives such as chlorine or ozone, become increasingly popular. This article explains in detail the differences between a natural pool and a conventional pool.
Plants for the phyto-purification of natural pools
Natural pools are fully-fledged ecosystems, where plants, in addition to their task of purifying and cleaning the water, create a beautiful natural environment.
Aquatic plants are selected to implement a phyto-purification process that allows the water to remain clean, clear and algae-free in a natural way.
There are three types of aquatic plants to include in a natural pool.
Marsh plants work in symbiosis with aerobic bacteria that are present near their roots. These bacteria are able to degrade organic pollutants, pathogenic bacteria, and even heavy metals. The marsh plants in turn feed on a part of the substances dissolved in water and the inorganic substances produced by the bacteria.
Submerged plants are the best when it comes to producing oxygen and, thanks to their leaf surface, they also allow more beneficial bacteria to settle in, thus allowing for greater purification efficiency.
Water lilies, in addition to decorating the natural pool and also performing phyto-purification, keep the water temperature under control, hindering solar radiation on a large part of the surface.
All together these three types of plants are essential to purify and oxygenate the water, preventing the formation of algae.
Here it is explained how to choose aquatic plants for a natural pool (and which ones to avoid like the plague).
There should be no fish in natural pools because their excrement would create more organic residues that would have to be purified, and therefore adding fish would be counterproductive.
The two systems for building a natural pool
There are two possible systems to build a natural pool:
- Traditional integrated purification natural pool (a bathing pool surrounded by a plant-filled area, a method mainly used in the past),
- Natural pool with separate vessels (with two separate vessels, one for bathing and another for phyto-purification).
Natural pool with separate vessels make it possible to achieve a higher water quality in the pool than traditional natural pools.
The phyto-purification vessel can be arranged around the bathing vessel, e.g. on two sides, or it can be a separate pond.
How to build a natural pool with separate vessels
In a natural pool with separate vessels, as the name suggests, the bathing vessel is separated from the phyto-purification vessel.
The bathing vessel and the purification vessel are on two different levels, so that the water can pass from one to the other continuously thanks to a small waterfall. Then the water returns to the other vessel thanks to a pump.
Usually, the purification vessel is placed a little bit higher, and the bathing vessel a little bit lower, so that a small waterfall can be appreciated while the water enters the bathing vessel.
The pump draws the water from the bathing vessel and sends it back to the plant zone.
In the purification vessel I recommend that you put a layer of gravel at the bottom (see details in the drawings below) and place the plants with field soil in micro-perforated baskets placed in the middle of the gravel (the baskets will not be visible as they must be covered by the gravel substrate).
The micro-perforated basket allows the roots to come out into the gravel substrate, improving the water purification efficiency, but at the same time keeps the plant’s expansion under control so as to make future maintenance easier.
Quantity and types of aquatic plants in a natural pool
Half of the surface area should be dedicated to plants, and half to the bathing zone. Let me give you an example. If you want to have a bathing zone of 100 square metres, there must be 100 square metres dedicated to plants.
You can choose the shape, but the important thing is that there is a recirculation so that the water enters on one side of the water purification pool, and exits on the other side, having necessarily gone through the whole plant area.
In addition, half of the surface of the purification zone should be dedicated to marsh plants and half to water lilies and submerged plants, which must be placed at two different depths (see diagrams below). Of course, this must be evaluated according to the available surface area.
If you are building a natural pool and you want to set it up quickly with the most suitable aquatic plants, we have created Phyto Natural Pool Kits, i.e. aquatic plant kits in which the species will be selected by our staff according to the characteristics and surface area of your natural pool.
Designing a natural pool with separate vessels
The use of one or more pumps is indispensable in natural pools. They must be energy-efficient in order to be able to run at all times, from spring till the end of summer.
In addition, depending on the result you want to achieve, there should also be pressure filters in a natural pool, which ensure greater water clarity and quick cleaning in the event of many people present for bathing (e.g. oily spots from sun creams, hair, etc…).
If you would like to build a natural pool, DIY Natural Pool is now available, our consultancy service that starts with a sketch on paper and accompanies you along the way until you take your first bath in your natural pool and beyond!
Here are two diagrams of a natural pool with separate vessels (zone with marsh plants, and zone with water lilies)
Here is a simplified example of layout of a natural pool with separate vessels
The arrows represent the direction of water recirculation and are only included as an example. The study of actual water flows is a subject of the DIY Natural Pool course.
How to build a traditional natural pool with integrated purification
The traditional natural pool looks like a pond to the eye; in fact, the bathing zone is separated from the plant zone only by a perimeter made of masonry, stones, wood, or soil covered with a PVC liner.
The surface area dedicated to plants should be at least twice the size of the bathing area, but depending on the presence or absence of biological filters and a water recirculation circuit, the surface area dedicated to plants may have to be increased by up to four-fifths of the total.
For example, out of 100 square metres, the area devoted to plants should occupy 67 to 80 square metres, depending on how the bathing pond is designed.
In addition, the area dedicated to plants should be distributed around the bathing area if possible.
We call this system Swimming Pond, as opposed to the separate pool system described above, which we identify with the actual term natural pool.
The bathing area can be e.g. 1.5 m deep, while the plant area must have a water depth of 10 cm in the marsh plant area, and 50/80 cm in the water lily area.
Of course you have to add the space for the substrate (about 30 cm of gravel) in which you are going to place the micro-perforated baskets filled with soil into which you are going to place the plants.
In this way the plants have the necessary soil to start vegetating by absorbing the nutrients of the soil, but the roots can later emerge from the basket, penetrating into the gravel substrate, thus allowing a more effective phyto-purification process.
The two areas can be separated by a submerged wall, which has to be, therefore, lower than the water level, so the water is free to flow from one side to the other.
I recommend using a pump to circulate the water between the bathing area and the plants area.
You can also pour the water taken from the bathing area into a drainage pipe (perforated) and pass it through the gravel under the planting area to force this water through the roots of the plants.
Here is a diagram representing a natural pool with integrated purification.
To learn more about and grow the three types of plants that are included in a natural pool, download the free “Guide to Growing Aquatic Plants“.
Effectiveness of phyto-purification in natural pools
I report the data of an experiment carried out by the University of Siena to demonstrate the effectiveness of phyto-purification in a natural pool.
Various bacteria in liquid solution (Escherichia coli, Staphylococcus aurius, Enterococcus faecalis, Cryptococcus laurenti) were introduced into a swimming pond with a volume of about 100 cubic meters of water and a purifying filter).
After being introduced into the pond, the pathogen load proved to be very high, while a sample taken 24 hours later showed a clear reduction in the pathogen load, which was almost completely eradicated after 90 hours.
The experiment, by the way, was carried out in the autumn period, a period in which the phyto-purification activity of the plants is reduced.
Diffusion of natural pools
Natural pools first appeared in Austria more than 30 years ago and finally in recent years have been gaining popularity throughout Europe.
Today, more and more people and public bodies become aware that the eco-pool, as opposed to a conventional pool, can be a solution that allows us to be healthier, more in touch with nature, and also with lower running and maintenance costs !
Here are the various reasons for building a natural pool.
To set up your own natural pool, please contact us via the channels indicated on the Contact page !
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