The importance of the antimicrobial activity of chitosan alsoarises when it is applied as a sorbent in filtering systems, whenfavorable environment for the growth of bacteria and fungiemerges by keeping the filtering material in the wet state.Biological fouling reduces fil-tration performance and shortens filter element life as well as cancause negative health effects. In order to increase the antimicro-bial resistance of sorbents, different means have been proposed However, the introduction of additionalsubstances possessing a biocidic activity, such as Ag, Zn, com-pounds etc., remains the main measure ensuring the biologicalsafety of water filtering materials.