You do not normally want to use bromine in disinfecting drinking water. In general, the brominated disinfection by-products are more harmful (more cancer-causing) than the chlorinated ones. For example, the brominated trihalomethanes (THMs) are all cancer-causing, but the solely chlorinated one, chloroform, is not except at very high cytotoxic levels. Also, use of BCDMH tabs will have leftover DMH (5,5-Dimethylhydantoin).
Most municipal water supply districts use chlorine for disinfection, usually from sodium hypochlorite (chlorinating liquid or bleach). Before you chlorinate, you want to remove as much dissolved organic matter as possible, usually through a combination of sedimentation (i.e. let still water settle), flocculation (adding chemicals to coagulate and settle), filtration (removal of insoluble compounds). Then after chlorination, many water districts add ammonia to form monochloramine when sending the water out into the lines. Monochloramine will last longer and produce fewer disinfection by-products in the lines on its way to homes and businesses.
