This invention provides concentrated aqueous biocidal solutions formed from bromine chloride, sodium hydroxide, and sulfamic acid. The weight ratio of bromine chloride:sodium hydroxide:sulfamic acid used in forming the concentrated solution is such that for every 10.5 to 11.5 parts by weight of bromine chloride used, 15.3 to 17.5 parts by weight of sodium hydroxide and 11.0 to 12.5 parts by weight of sulfamic acid are used, the biocidal solution containing at least about 100,000 ppm (wt/wt) of active bromine based on the total weight of the solution.
