Patent ID: 7699995

Claim:
A method for treating water in a closed cooling system, having a pH from 9 to 10.5 and a temperature of at least 35° C. and no more than 60° C., by adding a composition comprising 2-methyl-4-isothiazolin-3-one; wherein said composition is substantially free of metal ions non-aqueous solvents, volatile organic compounds and halogenated biocides; wherein metal ions, non-aqueous solvents, volatile organic compounds and halogenated biocides are not added separately to the water; and wherein 2-methyl-4-isothiazolin-3-one is present in an amount sufficient to produce in the water a 2-methyl-4-isothiazolin-3-one concentration from 15 ppm to 500 ppm to control the growth of microorganisms in said water.