Frequently allowing your potable water tank to empty completely, and occasionally sanitizing it will keep bacteria levels down. Filling your tank with city water actually helps sanitize it due to the treatment that the cities are required to give potable water. That being said, I personally do not use hook-up or tank water for drinking. We always carry an ample supply of filtered water from our house in empty gallon orange juice containers. IMHO you can't make a good pot of coffee with tank or hook up water.