Radon is the most harmful natural contaminant in the indoor atmosphere of the buildings. The noble gas, after cigarette smoke, is the biggest cause of lung cancer, and today the study of its diffusion, distribution, and concentration around the world has attracted many researchers in the field of radiation protection and environmental health. Typically, output data obtained from traditional methods of measuring radon concentration in indoor buildings is limited to information on the average radon concentration. Although these data are highly valuable in identifying buildings with a high risk of radon, it can be misleading to identify the real danger for residents of these buildings. This study aims to investigate the effects of water temperature and water flow rate on radon concentration and distribution inside the showers. Numerical simulations were conducted using CFD. Also, radon concentration in water was determined by the radon detector AlphaGUARD and is used as input in CFD simulation. The results showed that variations in the water flow rate have more influence on radon distribution than the changes in water temperature. Experiments were performed by measuring radon concentrations at different times in the shower room using monitor Radon Scout Plus. The annual effective dose of radon concentration in the shower room was also investigated.