Since late 2008, all SteriPEN water sensors feature twice the electrode voltage of older models. The increased electrical current flow allows proper function in water with low conductivity such as snowmelt and even mineral-free distilled water. SteriPEN Sidewinder Water Purifier Specs Specification Description Best use Backpacking Ultraviolet Protozoa, bacteria and viruses 16.6 ounces 8.6 x 5.5 x 3.8 inches 32 fl. oz. per 90 seconds Not applicable Not applicable Yes Ultraviolet light Not applicable Yes