The filtration system for fountains

Descrizione e analisi dei principali tipi di impianti di filtrazione per le fontane
The filtration system for fountains

Fountains are the piece of furniture that more than any other decorates and enhances spaces, whether public or private, internal or external, large or small: the charm of flowing water attracts people of all ages and instills serenity and well-being from the first sight. However, keeping the water clean and healthy is a professional job and not at all obvious, how many times have you seen fountains with dirty/green water or even full of algae? To avoid all this, a custom-designed filtration system is essential, taking into account the context, size and use of the fountain.

The filtration system of a fountain performs several crucial functions to guarantee the beauty and durability of the project, as well as the healthiness and safety of the water. Its importance in building or implementing a fountain cannot be underestimated: without an effective and well-designed filtration system, water quickly becomes an environment conducive to the growth of bacteria and other harmful organisms.

The primary function of the filtration system is the removal of contaminants from the water, such as debris, algae, bacteria and other organic materials that can accumulate in suspension or settle on the seabed: all these elements make the water green, smelly and unhealthy for the people and animals that use it. Furthermore, the filtration system helps to improve the circulation of the water in the fountain, which is essential to prevent stagnation and therefore the proliferation of pathogenic viruses and bacteria, but also more “trivially” the reproduction of mosquitoes and other insects that lay their eggs and complete the first stages of evolution in stagnant waters.

There are different types of filtration systems for fountains, available according to the specific needs of the project and its intended use. In general, they are divided into two macro categories:

  • with chemical filtration and therefore with the use of products such as acid and chlorine;
  • with biological filtration, where the filtration work is carried out in a natural way by a series of biological filters and colonies of “good” bacteria (not harmful to people, animals or plants).


Fountains with chemical filtration have the following components, which, however, may vary depending on the characteristics of the project:

  • mechanical filter: it is the main element of the filtration system and is designed to remove solid particles (debris and impurities) from the water. Mechanical filters can be of different types, such as glass grit or sand. In our projects we always use glass grit filters, because – compared to sand ones – they have a greater filtering capacity, given by the different diameters and the smooth surface that allow retaining a vast range of particles, a longer life and more quick and simple maintenance;
  • water recirculation pump: essential for the creation of the water feature, but even in the case of a reflecting fountain, minimal movement of the water is essential to enhance the aesthetic effect and avoid water stagnation waterfall;
  • panel for the control and automatic dosing of acid and chlorine: it is the indispensable element to ensure always clean and crystalline water in a fountain, because it constantly monitors the pH and Redox levels and releases acid and chlorine in the right quantities when needed, keeping the water values always balanced to avoid the formation of algae and limestone;
  • skimmer: an optional component, but widely used in outdoor fountains, because it acts as a pre-filter and removes leaves, twigs and other floating particles from the surface of the water.


Biological filtration is used in projects such as water gardens, fish ponds, lakes, bio lakes or bio pools, and in all aquatic creations that require the presence of plants and/or fish. The biological filtration has elements in common with the chemical filtration system, such as the recirculation pump and the skimmer, while the glass grain filter and the panel for the control and automatic dosage of acid and chlorine are replaced by the mechanical filter drum or sponge, biological filter and UVC sterilizer.

The mechanical drum or sponge filter is used to capture the smallest particles of dirt dissolved in the water, it is not present in all projects, but is prepared according to the amount of water to be filtered and the intended use.

The biological filter can be given by a modular system of the type:

  • Pressure filter: ideal for architectural pools, raised streams or ponds up to 30m2 with plants and fish;
  • Continuous modular pumping filter: to be installed in large projects (for example ponds up to 260m3) where the filter system is located in an elevated position with respect to the body of water;
  • Gravity modular continuous filter: also to be installed in large projects, but if the filter system is at the same level as the body of water.

The sterilizer or UVC lamp, also called germicidal lamp, is useful for eliminating suspended organisms harmful to the created environment and for breaking down the DNA of the alga, so that it can no longer reproduce.


The particularity of biological filtration is the use of beneficial bacteria to remove organic waste from the water. It is a complex process that takes place in two main phases:

  1. phosphorus (or phosphate) cycle: phosphorus is the primary nutrient of algae, through a process it is made unavailable, so the algae are deprived of their main nutrient and consequently cannot reproduce. The elimination of phosphates can be carried out through three methods, each obtained from a different ratio between aquatic plants for phytoremediation and filtering elements (100% plants / 30% plants and 70% phosless filter columns / 100% forced phosphate trap);
  2. cycle of nitrogen (or of nitrogenous substances): nitrogen is a marginal nutrient, but nonetheless important for the maturation of the water in the basin. Various organic deposits (such as leaves, insects, epidermis, hair, urine, drinks) dirty the bottom of the tank and the water: a small part is absorbed by bacteria that live in symbiosis with the roots of the plants, while the rest it is reconverted through biochemical reactions by strains of nitrifying bacteria of the genus Nitrosomonas or Nitrospiras.


As you have seen, a filtration system, whether for a fountain or a water garden, is made up of various components that work together to keep the water clean, crystalline and healthy. Once installed, it must be maintained regularly to ensure correct operation, therefore it is essential to establish a scheduled maintenance calendar.

The success of a project is given by the combination of technical design and careful maintenance, the “perfect combo” to guarantee the quality and functionality of the MEP parts and a high aesthetic value that lasts over time.


Susanna Dei Rossi

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