Any point-of-use or point-of-entry instrument or contrivance sold or offered for rental or lease for residential or commercial use, and designed to be added to the plumbing system, or used without being connected to the plumbing of a water supply intended for human consumption in order to improve the water supply by any means, including, but not limited to, filtration, distillation, adsorption, ion exchange, reverse osmosis, or other treatment.