In view of the present interest on grey water reuse, this paper describes the residual chlorine decay in grey water chlorinated samples. Several theoretical models were compared, resulting in a parallel first-order model with four adjustable parameters, which showed satisfactory adjustment to experimental data. According to this model, the added hypochlorite was divided into three fractions of different reactivity. A first fraction was rapidly reduced to stable compounds, such as chloride, without interest from a disinfectant point of view. Then, the remaining compounds with oxidative and disinfectant properties were differentiated into two other fractions of different reactivity, i.e., a higher reactive fraction which disappears in few hours, and a slower fraction which remains for several days. Kinetic parameters from 45 grey water samples are reported.