Aims: To develop a set of kinetic equations which more ably describe the disinfection process. Methods and Results: A group of functions, the fa(t) equations, based on the model used for the quantification of microbial inhibition, was produced. These functions introduce a limit to the numbers of micro-organisms capable of being disinfected. These new expressions were shown to be more general forms of currently-used (e.g. log-linear) disinfection models, and accommodate the lags and/or tails of non-linear log-survivor-time plots. An advance in the experimental procedures used to obtain disinfection data, using an optical density technique, was developed concomitantly. Conclusions: The methods of analyses (experimental and modelling) allow the researcher to examine, more ably, five-minute disinfection (or specific time disinfection tests) as well as the more important disinfection rate analyses. Significance and Impact of the Study: The fa(t) equations are an improvement over commonly-used rate models of disinfection, which are shown to be special cases of these equations. This raises the question as to whether our current understanding of the kinetic basis of disinfection requires revision.