TORUS PET Standard Filters use high quality activated carbon to remove impurities, to ensure your pet has access to clean, fresh, water. Our Standard Filters improve water clarity, reduced unpleasant odors, and removes chlorine, chloramine, tannins, phenol, hydrogen sulfide and some other compounds that cause odors Standard Filters comprise a molded cone with perforated walls which allow water to flow-through whenever your pet drinks and lasts for approximately one-month. So each replacement pack of six filters gives your pet approximately six-months of fresh, clean water.