The Storm Water Fee rate schedule is based on the impervious area of the property or unit that is being billed. Single-family residences are all charged based on one unit, currently $78 per year. The rate for non-residential properties is determined by calculating the impervious surface area on the property and dividing that number by the average impervious surface area for residential property; the result of that calculation determines the quantity of units that parcel is billed.