A type of municipal water rate structure charged by a community water system to those it supplies. With a flat fee, the use cost, which is usually additional to the base service fee, is instead included in the base service fee. The price may differ by user group, such as residential, commercial, and agricultural, but does not vary with the amount of water used. This type of municipal rate structure is common in communities that do not meter water use. Source: Understanding Your Water Bill | US EPA.