The invention provides the use of a water-soluble biocide as an uncoupling agent at an effective amount to control bacterial biomass in an aqueous system. The invention also provides a method for controlling the growth of bacterial biomass in an aqueous system. The method comprises adding to, or contacting with, the aqueous system an effective amount of an uncoupling agent which is a water-soluble biocide. In a preferred embodiment the method comprises contacting an effective amount of an uncoupling agent which is a water-soluble biocide directly with the bacterial biomass in an aqueous system.