A method of reducing a microbial load in a recirculating cooling water system in which cooling water circulates through a cooling water circulation loop including a heat exchanger where the cooling water is heated and a cooling tower where the cooling water is cooled for return circulation to the heat exchanger, and wherein the method comprises; circulating the cooling water through the cooling water circulation loop; removing a portion of the circulating cooling water from the cooling water circulation loop as blowdown to remove water as it becomes more concentrated in salt, scaling minerals, microbes and other chemicals and impurities; removing a portion of the circulating cooling water from the cooling water circulation loop through escape from the cooling tower in drift including mist or aerosol with water and dissolved and suspended solids, chemicals and microbes; and adding makeup water to the circulating cooling water in the cooling water circulation loop to make up for water lost to evaporation, the drift and the blowdown; the method characterized by: injecting a peracetate oxidant solution into contaminated circulating cooling water in the water circulation loop, the contaminated circulating cooling water containing a population of microbes, and contacting in the cooling water circulation loop the contaminated circulating cooling water with the peracetate oxidant solution; mixing said contaminated circulating cooling water with the peracetate oxidant solution in the cooling water circulation loop to form a mixture; wherein, the peracetate oxidant solution, as injected into the contaminated circulating cooling water, comprising: a pH from pH 10 to pH 12, peracetate anions and a peracid, with a molar ratio of peracetate anions to peracid ranging from 60:1 to 6000:1; and a molar ratio of the peracetate anion to hydrogen peroxide greater than 16:1; and separating the mixture into at least microbes and a water phase. circulating the cooling water through the cooling water circulation loop; removing a portion of the circulating cooling water from the cooling water circulation loop as blowdown to remove water as it becomes more concentrated in salt, scaling minerals, microbes and other chemicals and impurities; removing a portion of the circulating cooling water from the cooling water circulation loop through escape from the cooling tower in drift including mist or aerosol with water and dissolved and suspended solids, chemicals and microbes; and adding makeup water to the circulating cooling water in the cooling water circulation loop to make up for water lost to evaporation, the drift and the blowdown; the method characterized by: injecting a peracetate oxidant solution into contaminated circulating cooling water in the water circulation loop, the contaminated circulating cooling water containing a population of microbes, and contacting in the cooling water circulation loop the contaminated circulating cooling water with the peracetate oxidant solution; mixing said contaminated circulating cooling water with the peracetate oxidant solution in the cooling water circulation loop to form a mixture; wherein, the peracetate oxidant solution, as injected into the contaminated circulating cooling water, comprising: a pH from pH 10 to pH 12, peracetate anions and a peracid, with a molar ratio of peracetate anions to peracid ranging from 60:1 to 6000:1; and a molar ratio of the peracetate anion to hydrogen peroxide greater than 16:1; and separating the mixture into at least microbes and a water phase. injecting a peracetate oxidant solution into contaminated circulating cooling water in the water circulation loop, the contaminated circulating cooling water containing a population of microbes, and contacting in the cooling water circulation loop the contaminated circulating cooling water with the peracetate oxidant solution; mixing said contaminated circulating cooling water with the peracetate oxidant solution in the cooling water circulation loop to form a mixture; wherein, the peracetate oxidant solution, as injected into the contaminated circulating cooling water, comprising: a pH from pH 10 to pH 12, peracetate anions and a peracid, with a molar ratio of peracetate anions to peracid ranging from 60:1 to 6000:1; and a molar ratio of the peracetate anion to hydrogen peroxide greater than 16:1; and separating the mixture into at least microbes and a water phase. a pH from pH 10 to pH 12, peracetate anions and a peracid, with a molar ratio of peracetate anions to peracid ranging from 60:1 to 6000:1; and a molar ratio of the peracetate anion to hydrogen peroxide greater than 16:1; and separating the mixture into at least microbes and a water phase.