Our advanced proton exchange membrane technology is compatible with all varieties of potable water. Including: Unfiltered tap water, filtered water, reverse osmosis (RO), natural spring, purified, and even well water. If you use hard water (i.e. tap or well) - please make sure to descale your water at least once a month to lengthen the life of the product. For instructions, please see "How Do I Clean My Bottle" above.