The invention is a process for preventing microbial growth in aqueous streams by applying a C.sub.2 -C.sub.12 percarboxylic acid or mixture of such acids to the aqueous stream and to an automated dispensing system for the percarboxylic acids based on a correlation between oxidation-reduction-potential and anti-microbial levels of the aqueous stream. Generally, the process of the invention is applicable to aqueous streams used in any number of applications such as the application of streams for the transport of food products, e.g. fruits or vegetables, into the processing environment and through the various steps of processing.