the present invention is directed to a biocidal water treatment composition , water treatment apparatus , and method of treating water to reduce levels of pathogens . the composition contains sources of copper , zinc , and silver metal ions within a crosslinked polymer matrix . examples of these ion sources include copper sulfate , zinc sulfate , and silver nitrate . an example of the crosslinked polymer matrix is crosslinked chitosan , which also serves to clarify the water and release the metal ions over time . the product is easy to manufacture , and allows the use of decreased halogen sanitizer , as well as decreased copper ion , thereby decreasing the likelihood of staining . the product simultaneously provides good bactericidal and algaecidal properties , despite low levels of copper ion and low chlorine levels .