The Oxygenated Water Treatment (OT) was evaluated under conditions of worsening feedwater quality. The after-cation conductivity was adjusted to 0.1, 0.2, and 0.4 μ S/cm using NaCl solution. Temperature conditions were 100, 200, and 355°C. The results showed that the iron release rate was influenced by operating temperature and water quality. In particular, lower temperature (100°C) and worsening water quality required a longer time to produce passivity film. In the case of temperature conditions of 200 and 355°C, we could not confirm any differences in passivity film formation time.