The invention relates to a method of installation of a modular well screen (underground water filter) in a borehole and a well screen module, and it is characterizing in that casing pipe (4) sections are filled with water at least in their horizontal segments, whereas the well screen modules (10) contain removable displacement elements (10.5) having adjustable displacement, which elements are connected one to each other mechanically by means of mechanical catches (10.7), as well as pneumatically by means of pneumatic fasteners (10.8), and wherein the last displacement element (10.5) is connected to a winch and to a compressor on the surface (the ground surface).The air pressure in the displacement elements (10.5) is adjusted using the compressor, while inducing a buoyant force that balances or reduces the weight of the well screen modules (10) and extraction pipes (6), in such a way as to minimize resistance to motion in the process of they being inserted into the casing pipes (4) positioned in the borehole. Upon the installation is completed, the displacement elements (10.5) are removed.