Potable water is safe for consumption. This water has been properly treated so that it is safe for drinking, bathing, and cooking.
Non-potable water is NOT safe for consumption. This is water that either did not go through the same treatment process as potable water or it has been properly treated but has since become contaminated. Many factors can make potable water become non-potable, such as exposure to chemicals, gases, pollution, infective agents, or any other contaminant.