This article establishes the efficiency of a single-circuit thermosyphon domestic solar hot water system for Polish cities such as Warsaw, Lublin, Bialystok, Czestochowa and Szcze- cin, using two indicators, namely the solar share and the efficiency of solar collector. It was found that of the selected cities, Bialystok is the most attractive in terms of using solar energy for hot water supply systems, as the solar hot water supply system has the highest solar share f = 0.64, and the efficiency of the solar collector is  = 0.553. The lowest effi- ciency of the solar hot water supply system is observed for the city of Szczecin, which is characterized by indicators f = 0.49 and  = 0.505, respectively. These analytical studies show that the use of the solar hot water system in selected cities in Poland can save on traditional energy sources for hot water systems by up to 50%.