This invention relates to a method for preparing a stabilised stock hypobromous acid solution, and to a stabilised stock hypobromous acid solution. The stabilised stock solution has a hypobromous acid concentration of less than 30% (m/m) and contains an amount of cyanuric acid as a stabiliser not exceeding 1 ppm. The solution may be used for treating any type of water, but has particular application in treating drinking water and irrigation water.