Infection cases have been reported where Legionella spp. and NTM (non-tuberculous mycobacteria) increased due to the contamination of circulating water in cold/heated water supply systems for extracorporeal circulation used in cardiac surgery and ECMO (extracorporeal membrane oxygenation) for blood temperature regulation. The contaminated circulating water became aerosolized and may have been a source of infection. The internal structure of these systems is complex, making it difficult to clean and disinfect the inside of tanks and piping, posing a risk of becoming a breeding ground for bacteria. However, contamination and environmental exposure risks have not been clearly understood. Therefore, we conducted an experimental investigation to evaluate the potential spread of NTM from the circulating water to the surrounding environment, using Mycobacterium fortuitum as a test organism and confirmed that Mycobacterium was dispersed into the air during system operation and when opening the cover of the cold/heated water tank for water supply. It is urgent to establish methods to maintain effective cleaning and disinfection of cold/heated water supply systems for extracorporeal circulation and to implement operational improvements, such as enhancing the sealing of water tank covers, minimizing the opening of water tank covers during operation, and isolating the system in the operating environment.