A method of microbial control in water comprising adding to the water one or more bromine-based biocide(s) and cis-2-decenoic acid or a salt thereof, wherein said bromine-based biocide is selected from: A) a non-oxidizing bromine-based biocide selected from the group consisting of: A1)2-bromo-2-nitro-1,3-propanediol (Bronopol) and A2) 2,2-dibromo-3-nitrilopropionamide (DBNPA); B) an oxidizing bromine-based biocide selected from the group consisting of: B1) 1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH); B2) an on-site oxidized bromide source, which releases active bromine species in water; and wherein the on-site oxidized bromide source is selected from: sodium bromide, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; HBr, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; ammonium bromide, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; solution of HBr/NaBr and urea, which reacts with hypochlorite, chlorine or electrochemically on-site to produce the bromourea active form, to be added to the water system to be treated; and B3) sulfamate stabilized aqueous solution of alkali hypobromites (bromosulfamate). A) a non-oxidizing bromine-based biocide selected from the group consisting of: A1)2-bromo-2-nitro-1,3-propanediol (Bronopol) and A2) 2,2-dibromo-3-nitrilopropionamide (DBNPA); A1)2-bromo-2-nitro-1,3-propanediol (Bronopol) and A2) 2,2-dibromo-3-nitrilopropionamide (DBNPA); B) an oxidizing bromine-based biocide selected from the group consisting of: B1) 1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH); B2) an on-site oxidized bromide source, which releases active bromine species in water; and wherein the on-site oxidized bromide source is selected from: sodium bromide, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; HBr, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; ammonium bromide, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; solution of HBr/NaBr and urea, which reacts with hypochlorite, chlorine or electrochemically on-site to produce the bromourea active form, to be added to the water system to be treated; and B3) sulfamate stabilized aqueous solution of alkali hypobromites (bromosulfamate). B1) 1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH); B2) an on-site oxidized bromide source, which releases active bromine species in water; and wherein the on-site oxidized bromide source is selected from: sodium bromide, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; HBr, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; ammonium bromide, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; solution of HBr/NaBr and urea, which reacts with hypochlorite, chlorine or electrochemically on-site to produce the bromourea active form, to be added to the water system to be treated; and sodium bromide, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; HBr, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; ammonium bromide, which is oxidized on-site with hypochlorite, chlorine or electrochemically to produce its active form, to be added to the water system to be treated; solution of HBr/NaBr and urea, which reacts with hypochlorite, chlorine or electrochemically on-site to produce the bromourea active form, to be added to the water system to be treated; and B3) sulfamate stabilized aqueous solution of alkali hypobromites (bromosulfamate).