A water cleaner comprises: a filtering canister having a plurality of filtering holes formed through the canister and made of oxidation-reduction alloy for filtering off chlorine and other hazardous materials contained in the water when passing through the filtering holes formed through the canister; and a functional water-treatment material filled in the canister for killing bacteria or fungi, for removing pollutants, and for removing odor in the water for cleaning water in a water tank or reservoir.