Abstract: The present invention discloses the use of an electrolysis cell (30,40,50-52) to provide for super chlorination of cooling tower water. Halogens naturally present in the water are concentrated by evaporation and provide the starting material for the production of oxyhalite compounds (typically to a level of superchlorination) as a biocide. The biocide is recycled thereby avoiding the cost of chemicals. The level of atmospheric polluants, and particulate matter especially, is thought to be the determining factor in biocide consumption.