An Equivalent Residential Unit is a billing unit for the amount of storm water runoff from the impervious area of the average-sized residential parcel. It is a measure that serves to compare runoff generated by different size and type of properties with different storm water generation characteristics. In North Miami Beach, an ERU represents 1,800 square feet of impervious surface that is found on the property.
Residential properties are billed based on the number of dwelling units, therefore a single-family home is charged for 1 ERU. Multi-family dwellings of 3 units or more are charged for 0.75 ERU per unit.
A commercial property with 3,762 square feet of roof plus parking area would have a storm water runoff Equivalent Residential Unit area equal to 2.09 ERU (3,762 divided by 1,800).