A water treatment apparatus includes a storage unit storing water to be treated including a pharmaceutical drug, an apply unit applying the water to be treated to the storage unit, an addition unit adding into the water to be treated metal salt generating halide ions when dissolved in the water to be treated, and an energizing unit applying a current to a pair of electrodes immersed in the water to be treated in the storage unit. The pharmacological activity of the pharmaceutical drug is eliminated or reduced by decomposing or altering at least a portion of the chemical structure of the pharmaceutical drug included in the water to be treated through electrolysis.