Abstract: This invention relates to the discovery that chemicals existing in natural waters, which have been pretreated in municipal water treatment facilities, as well as natural surface and underground waters which have not been so pretreated, do inhibit the biocidal effect of known water disinfectants of the metallic ion type. This may be overcome by exchanging for the halide ions in such water an anion, such as bicarbonates, which does not inhibit the biocidal effect of metallic ions, nor does it react chemically with known oxidizing biocides to form halogenated organics which are suspected of causing cancer. Further, water treated in accordance with this invention substantially maintains its original ionic character to maintain the water in a natural state, for example, not deionized.