“The checks confirmed he had been infected with the bacteria,” director of the municipal hospital in Rzeszow Grzegorz Materna told state news agency PAP.
According to the local authorities, 71 people were admitted to hospitals with legionellosis infection.
The authorities in Rzeszow have called in an emergency meeting to determine the cause of the contamination which is not yet known.
All four victims were elderly people.
Legionellosis causes pulmonary issues, especially for people with weak immune systems.
Local officials announced additional disinfection works and checks in the municipal water supply network, with the first sample results to be known Monday.
Legionnaire’s disease is not contagious and cannot be spread directly from person to person, but can multiply in water and air-conditioning systems.