Described are highly concentrated liquid biocidal solutions formed in water from (a) specified bromine sources (e.g., BrCl or mixtures of BrCl and Br2) and (b) alkali metal salt of sulfamic acid and/or sulfamic acid and alkali metal base, wherein the solution contains >160,000 ppm of active bromine. Solutions of this type have been found to have greater stability than a commercially-available solution made from the same components containing 148,600 ppm of active bromine. Also described are new, water-soluble, solid state biocidal products formed by removing the water from solutions made in water from (a) and (b) irrespective of the initial concentration of active bromine. Removal of water can be accomplished by flashing or distillation at reduced pressure or preferably by spray drying. Such solid state products are typically in the form of powders or small particles, but can be compacted into larger forms preferably with the aid of one or more suitable binding agents.