EDITION: April - June 2022

Natural swimming pools

By María V.R.
The hot summer season is coming soon, and many people are thinking about adding a swimming pool to their home, or renovating an existing pool. After all, what could be more refreshing than diving into the crystal clear water of your own pool. In most pools that beautiful water is kept free of bacteria and fungi by using chlorine and/or other chemical agents, however there are also more natural ways to keep your pool pristine. One alternative is to build a natural swimming pool – also known as an eco-pool or bio-pool – to create clean and clear water with an ecological purification system. This type of pool is designed to be a self-contained aquatic ecosystem that uses the filtering capacity of plants, gravel and sand. Not only is it free of chemicals, but it also has a wonderfully natural look that can enhance the beauty of your property. 

All swimming pools need a purification system because without one the pool accumulates algae. This initially makes the water look cloudy, and if untreated it creates pathogens that are detrimental to health. In order to achieve good water quality you need to remove the organic matter that the algae feeds on. In ecological pools this is done naturally by creating a system that is based on the way that water is cleaned in nature. An eco pool is divided into three areas: the swimming pool, the regeneration area and the filtration system. The system is intended to imitate nature, so the water needs to be in constant circulation as in a river. This can be done through a system of pipes, pumps and waterfalls. The water continually passes through each area of the system, just as it would in the bed of a river: from the swimming area, to the regeneration zone, to the filtering area and then back to the swimming area.

Let’s start by looking at the swimming area which has a waterproof elastic base that becomes invisible once the construction is finished. It is necessary to create a current in the pool that circulates the entire volume of water through the regeneration and filtration systems two to four times each day (depending on the size of the pool). The water passes from the pool into the regeneration zone which contains a variety of gravels and aquatic plants. This makes it very similar to a miniature wetland, and here is where the purification begins. The combination of gravel and special plants eliminates polluting organic elements while absorbing excess nitrogen and phosphorus. The plants are selected based on their compatibility with the local climate. Some project their beauty onto the surface of the water like water lilies, while others only reside on the bottom. Reeds, hyacinths and duckweed have an especially high capacity for cleansing the (eutrophic) water.

Fully regenerated, the water then passes into the filtration zone which is based on nature’s simple system – the same process by which rainwater filters through the ground before it reaches underground aquifers. The filtration zone is made primarily with pebbles and sand that are layered to naturally filter the water as it passes through. In most cases other types of filters are added at the end of the process to further enhance the quality of the water as it flows back into the swimming pool. Because there are no chemicals in the water it has a quality that is lighter and more transparent than in conventional pools. 

Natural pools have been popular in Austria, Germany and England for decades, but these are countries with relatively few pools as swimming is possible only a few months of the year. Here in Spain, where we have many more pools due to the warmer climate, bio pools have only recently begun to gain favour. The initial investment to construct a natural pool is higher than for a conventional one, but this is partially offset by reduced maintenance costs. However, the real value is in the enjoyment and health benefits of swimming in water that is naturally clean and free of chemicals. Add in the aesthetic value of a beautiful pool that is integrated in harmony with the landscape, and it is easy to see why natural pools are destined to become ever more popular. 

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