In this paper, a stormwater fee specifically for small municipalities was developed through a simplification of the Equivalent Residential Unit (ERU) system, which is the main method applied in the United States. The Simplified ERU is based on the amount of impervious area and the fee considers the operations and maintenance costs, besides having a single class of billing. It was applied in Santo Amaro da Imperatriz city, located in the southern region of Brazil, which can be classified as a small city. The value of the Simplified ERU (294.32 m2) was similar to the average impervious area in the United States (269.42 m2) and it was equivalent to $0.28 per square meter (within the range of other countries' fees). The method proved to be a feasible and rapid technique for funding stormwater services, and its simplicity allows its application in different locations. This funding model can generate revenue to address current stormwater problems, such as the lack of funding for existing drainage infrastructure, and contribute to downstream flooding reduction. This paper also intends to encourage discussion about the methods for designing a stormwater fee in the academic community, which is still incipient.