Bromine, a less volatile compound than chlorine, is used as a sanitizing agent in drinking water systems, swimming pools, and spas.

The Colorimetric Method. The DDPD reagent, a methyl-substituted form of DPD, is employed. Potassium iodide is added to the sample before analysis. Bromine reacts with the iodide to liberate iodine. The iodine reacts with the DDPD reagent to form a blue-violet color. Results are expressed in ppm (mg/L) bromine as Br₂.