1.1 ,This test method covers the on-line and in-line determination of dissolved ozone (DO₃) in low conductivity water in the range from 0.001 mg/L to 5.0 mg/L DO₃ and conductivity <,100 μ,S/cm, typical of pharmaceutical and microelectronics pure waters. DO₃ is detected by correlating the response of a membrane-covered electrochemical sensor to the dissolved ozone concentration.