Hospital guidelines say 28–30 days. Many community members use it longer (up to 90 days) with proper technique (alcohol swab before and after each use, store in the fridge or at room temperature in a cool dark place). Janoshik testing has shown that BAC water begins to show measurable alcohol oxidation around 90 days, with ~8% alcohol drop by 120 days at room temperature. 90 days is the practical community cutoff.