Here is a better definition:
The term Equivalent Residential Units (ERU) originates from Land Use Regulations and is a legal term. The term is typically defined in a municipal ordinance dealing with land use.
The ordinance also employs the concept of equivalent residential units (ERU). Under the ERU approach, if the demand for public facilities created by a proposed development is equivalent to that of one dwelling unit, then the development is subject to the ordinance. The APFO applies to water, sewer, roads, and schools.
As communities struggle with mushrooming municipal growth, they are using a variety of tools to manage where, when, and how such growth will occur. One of these tools is concurrency regulations or adequate public facility ordinances (APFOs). An APFO is a land use regulation that is designed to ensure that necessary public facilities and services to support new development are available and adequate, based on adopted level of service standards, at the time that the impacts of new development occur. APFOs are designed to manage the timing, not the location or quality, of new development. Actual concurrency regulations will be different in each community depending on local planning needs and local law. One thing is clear, however; concurrency regulations are more advantageous than other traditional land use controls because they are more flexible and deal directly with population levels and employment growth, thereby controlling roadway demand. While they will not stop growth, down zone property, deter economic development, or raise housing prices; nor are they a catchall solution to growth management. They are one tool in the planning toolbox to help a community meet their expectation of growth and visions for the future.
Municipal utilities also use the ERU for billing purposes.
See the attachment.
