The biocidal polymers poly[ 1,3-dichloro-5-methyl-5-(4'-vinylphenyl)hydantoin] and poly[1,3dibromo-5-methyl-5-(4'-vinylphenyl)hydantoin] and the monochlorinated derivative have been prepared as insoluble porous beads. Halogen stability, rechargeability, and efficacy against pathogens (Staphylococcus aureus, Escherichia coli 0157:H7, MS2 virus, and poliovirus) in a water filtration application have been evaluated. While the polymers previously prepared in powdered granular solid form were effective against a wide variety of pathogens in contact times of a few seconds, the flow rates of water through cartridge filters containing them were often diminished because of clogging problems. Furthermore, the fine particles could be partially aerosolized in a manufacturing facility, thus causing a potential hazard for workers in the facility. The porous beads, prepared entirely by heterogeneous reactions, overcome these limitations while maintaining outstanding biocidal efficacies. The chlorinated beads have the potential to be used for disinfecting potable water in remote areas. The brominated beads are being evaluated as biocides for use in recirculating water applications such as for spas.