Water is considered safe to drink if it came from a natural source (river, lake, spring, groundwater) and it meets or is better than all of the federal, state, and provincial standards that are legally enforceable. In the United States, if your tap water does not meet any one of the standards, according to the law, your water supplier must notify all its customers as of the problem. Water is called potable when it is safe to drink. "Potable" rhymes with "floatable".