Filtration systems or underground modular tanks are rainwater management systems, the use of which mitigates the negative effects of soil sealing. They collect water from hard, impermeable surfaces, which can then be used to naturally enrich the aquifer, supporting the natural water cycle.

In this way, runoff filtration is slowed down, since the water is retained as much as possible in the system, thus avoiding the tidal peak and the consequent urban flood phenomena. In addition, stored rainwater, can not only be used to enriching the subsoil, but also can be used for secondary uses such as watering gardens, washing cars, or replacing drinking water in toilet flushes.

This modular structure is lightweight and ensures 95% water storage in the empty space. The boxes are made of PP and ensure long service life. Installation is a relatively simple process. First the pit is created and a layer of fine-grained sand is placed. Then, depending on the final use of the water to be disposed of, suitable geotextiles and/or geomembranes are used for filtration. Filtration boxes are then placed in the pit based on the original dimensioning. The whole system is "coated" with the geotextile and/or geomembrane and is covered with sand.

The underground installation of the system allows surface landscaping even if heavy vehicle crossings are required.