It is important to manage the residual disinfectant concentration as a countermeasure against Legionella for circulation bath. Based on the experimental data, this report examines that the differences of measuring results by absorption spectrometry which are used for determination of chlorine dioxide concentration. As a result, the simple DPD measuring device could be measured in the high precision like a spectrophotometer which went at a laboratory. Bath water however, the simple DPD measuring device could be measured in the high precision like the tap water. And it found that it was possible to use as a chlorine dioxide concentration measuring method which uses the simple DPD measuring device on fields. When measuring chlorine dioxide concentration, the influence of free residual chlorine can restrain a glycine by adding it.
