Poland belongs to the countries with limited waters intended for drinking resources. To meet this problem, the Management Board of Geotermia Mazowiecka SA carries out activities to determine the possibilities of using exploited geothermal waters other than energy purposes. In addition to energy, the geothermal water is used for recreation and balneotherapy in “Termy Mszczonów” and for the production of drinking water for the local water supply system. Some water needs to be discharged into surface watercourses due to a lack of coherence of heating and water supply needs. For recognizing this problem innovative research project entitled: “The development of a method for injecting after energy-used geothermal waters into selected geological structures” was prepared and implemented as part of the Regional Operational Program of the Mazowieckie Voivodship for 2014–2020 (Priority Axis: Research and development activities of enterprises). This project has resulted in the launch of the installation pumping excess water to the quaternary sandy leyer. Based on the results from the first year of operation of the project, it can be assumed that it is possible to achieve nearly 100% reduction of water discharge and, consequently, the full use of producted geothermal waters. In summary, it can be stated that the geothermal plant in Mszczonów is a unique installation not only on the Polish but also international scale. The proof of this is not only the scale of rational use of water for energy purposes (cooling from 41°C to about 17°C), but also their development in other areas, for example in “Termy Mszczonów” and for the production of waters intended for drinking. The article presents the results of the first year (2019) of operation of the water injection system. During this period, in cooled water discharged into surface watercourse nearly 50% reduction was achieved.