Glossary of Terms

Commercial Unit

A utility billing classification used to describe other developed land such as commercial, industrial, and non-profit properties (including churches, schools, land, and community service organizations).

Equivalent Residential Unit (ERU)

A unit of measurement for determining the stormwater utility fee for detached dwelling unit properties and other developed properties. For Alcoa, one ERU equals 2,696 square feet.

Exempt Properties

A utility billing term used to describe properties in the city that are exempt from paying a stormwater utility fee.

Impervious Surface

Surface areas that do not absorb rainfall resulting in stormwater runoff (i.e. roofs, patio areas, driveways, parking lots).

Residential Unit

A utility billing classification used to describe detached dwelling unit properties and multiple dwelling unit properties.


Rainwater that may be mixed with pollutants (oil, detergents, pesticides, fertilizers, sediments) that flows across impervious surfaces, travels through a drainage system, and ends up in our streams and rivers.


The flow of water that results from precipitation and occurs immediately following rainfall or as a result of snowmelt.

Stormwater Utility Fee

A fee calculated based on the amount of impervious surface area on a property. See the Stormwater Fee Schedule Page.

Stormwater Utility Fee Credits

A discount on stormwater fees for Commercial Units that complete an application and documentation describing best management practices that qualify based on the proportional benefit to the stormwater system. (i.e. stormwater and environmental curriculum for Alcoa City Schools).