A apparatus and method for killing microorganisms in a body of water that has been treated with ozone in the presence of bromide ions with the method comprising the steps of carrying out the ozonization of a body of water in the presence of bromide ions, adding a metal ion donor to the body of water, and adding a hypobromite ion scavenger to the body of water to interact with the metal ion donor to enhance a metal ion concentration in the body of water while suppressing the oxidization of the bromide by the Ozone to produce bromate.