Recently, the accidents caused by Legionella species have became a serious problem at public baths. To solve the problem, it is necessary to keep the residual chlorine in water at predetermined level by disinfectant. In this study, we aimed to understand the situation of chlorine disinfectant decrease in air bubble bath and ultrasonic bathtub. As the experiment conditions, we controlled to change water depth, amount of air, water temperature, volume of circulating water, gauge of air nozzle, and so on. In order to evaluate the behavior of disinfectant in water, the divergent coefficient was used to observe the decrease in the level of disinfectant over time. Regarding of the behavior of disinfectant in water in the bubble air bathtub and Whirlpool bathtub, the results were obtained respectively.