Combination biocide products are finding increased use in cooling water systems as an effective means of providing consistent microbial control under a wide variety of conditions. The use of two biocides gives broader spectrum control than using one product alone and also limits the potential of tolerance development with one treatment active. Optimum protection can be achieved when one biocide is applied continuously and the other intermittently. An effective biocide combination is glutaraldehyde, fed on a slug dose basis, concurrent with a low
level continuous use of DBNPA, conveniently added via a solid tablet. Select case histories, including comparative biocide treatment programs, will be presented as well as efficacy results from laboratory studies, including data on Legionella control.