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, impervious surfaces, which can then be used to naturally enrich the aquifer, supporting the natural water cycle.

In this way, the infiltration of the runoff is slowed down, since the water is kept as much as possible inside the system, with the result that the tidal peak and the subsequent urban flooding phenomena are avoided. In addition, the stored rainwater, apart from enriching the subsoil, can also be used in secondary uses such as watering gardens, washing cars, or replacing drinking water in cisterns.

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

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