Devices and methods for inactivating microbiological contaminants in a fluid are provided for use in water, air, and other fluid treatment applications. The device includes (i) a housing having at least one fluid inlet and at least one fluid outlet; and (ii) an antimicrobial material secured in the housing between said at least one fluid inlet and said at least one fluid outlet. In one embodiment, the antimicrobial material is a biguanide dihydrate compound, such as a chlorhexidine dihydrate, which exhibits broad spectrum antimicrobial activity.