At a time when biophilia is highly valued in architecture, natural pools become another element capable of increasing the connection with nature, enabling the creation of a recreational and contemplative space at the same time. Also known as ecological or biological pools, they reproduce an ecosystem composed of plants, rocks and even some species of fish.
The term “natural” is related to the type of treatment that the pool water receives, which, in this case, is free of chemicals. In this sense, its operation is similar to that of a natural lake, since each component has its function in the system: stones and sand retain impurities, plants promote water oxygenation and fish collaborate with the cleaning of the water, helping to eliminate larvae and insects. Basically, the natural pool is self-cleaning, and natural agents eliminate the need for chemical products, generating a self-sufficient, economic and sustainable maintenance cycle.
Replacing the traditional tiles and chlorine buckets, natural pools require a minimum excavation of 1.50 meters deep, and can be built in different shapes, therefore, the recurrence of organic forms dug directly into the natural soil and in small spaces, depending on the possibilities of the terrain. Immediately after excavation, a geotextile cover and rubber blanket – both non-toxic materials – are applied in order to retain water. The base of natural pools is usually composed of a type of white sand, including natural stones such as pebbles.
As an example of practical application, in the project of MS House by Studio Arthur Casas, a kind of artificial lake was created. It embraces the entire building and alleviates the arid climate of the interior region of São Paulo. Full of fish and plants, the lake turns into a natural pool in the area close to the social area of the house.
Although they are already very present in residential projects in European countries and the USA, in Brazil, this system has only recently received attention. In this sense, Brazilian companies specialized in the installation of natural pools claim that – unlike in other countries – there is a great demand for the crystallinity of the water. Therefore, to achieve this goal, filtration systems are inserted focused on large dirt particles, such as leaves, preventing the water from becoming turbid. In addition to the filter, it is also recommended to use hydraulic pumps to assist in the flow of water, but which, in this case, save 30% of energy compared to conventional pools. Another advantage of natural pools is maintenance, since, as they do not require chemical components, their conservation is very simple, limited to changing the filter every six months. It is also worth mentioning that the water from the natural pool can be reused for irrigation, which promotes a beneficial partial exchange of water and eliminates the need to build a cistern for this purpose.
In the project of Boathouse, by the Indian practice Architectonica Procreate, we chose to create a natural pool built with the aquaponics system, creating a space to swim in the midst of nature. Its delicate ecosystem is composed of aquatic plants, fish, frogs, turtles and migratory birds, and its architecture is a silent witness to the unfolding of this life.
In Canada, however, the application of the natural pool reached a larger scale, being used for the implementation of the public swimming pool Borden Park, an aquatic club with capacity for 400 bathers. In this daring system, filtration is done in two ways: through a biological-mechanical system or through the crushed stone and gravel filter built in situ with the Zooplankton.
Despite representing a slightly higher implementation cost than conventional pools and requiring specialized labor for their construction, natural pools can become an interesting alternative to contribute to local ecosystems, interrelating different species, including birds and insects, improving the air quality and microclimate of the region. In addition, many studies already prove how beneficial contact with nature is for humans, reducing anxiety and stress levels.
