The language below is for informational purposes only and is subject to change at any time. For official definitions and rules, see the City’s Stormwater Ordinances and Regulatory Documents & Tools.

The base fee for a Single Family Residential Unit is $13.32 per month. Other properties are assessed based on the amount of impervious area on the property. See Undeveloped or No Bill Properties or Non-Single-Family-Residential for details.

Impervious area is any surface, like the parking lot in the picture, which stops or reduces the amount of stormwater that soaks into the ground after a rain.

Important Notice

Impervious areas can include:

  • Rooftops
  • Sidewalks
  • Walkways
  • Patio areas
  • Driveways
  • Parking lots
  • Storage areas
  • Compacted gravel and soil
  • Awnings

Equivalent Residential Unit (ERU) = 2,454 sq. ft.


The City of Columbia’s Stormwater Utility Fee came into effect on July 1, 2002 and was updated effective July 1, 2017. All monies collected from this utility fee go strictly to fund stormwater related activities such as:

  • Designing and constructing capital improvement drainage projects,
  • Routine cleaning, maintenance and repair of the City’s stormwater drainage system,
  • Developing an inventory of the City’s stormwater drainage system,
  • Master planning for capital improvements, and
  • Complying with the City’s National Pollutant Discharge Elimination System stormwater quality requirements.

Stormwater runoff is water that flows over yards, streets, buildings, parking lots and other surfaces when it rains. Stormwater runoff eventually empties, untreated, into our local rivers, ponds and lakes.

As properties are developed, stormwater runoff increases. This increase has negative impacts on both the City’s storm drainage system and on natural drainage-ways which is directly proportional to the impervious area found on the developed property.

For stormwater billing purposes, the impervious area of a property are those surfaces that prevent or impede the infiltration of stormwater into the soil as it entered in natural conditions prior to development. Since the amount of stormwater runoff generated by a given property is directly proportional to the property’s impervious surfaces, the stormwater fee for a property is also directly proportional to the impervious area of the property.

The City of Columbia has established an Equivalent Residential Unit (ERU) for stormwater billing purposes. One ERU is equal 2,454 sq. ft., the average amount of impervious area found on a typical single-family residence*.

*This value was found using aerial photography of the area.

Property Fee Categories

Undeveloped or No-Bill Properties

Since a property’s stormwater fee is based on the amount of impervious area, those properties which are undeveloped or have no impervious surfaces will not be billed a stormwater fee.

Also, those non-single-family residential properties which have less than 600 square feet of impervious surfaces on them will not be billed a stormwater fee.

Single Family Residential

All of those properties which have only a single-family house, duplex, patio home, or mobile home on them are classified as Single-family residential. For stormwater billing purposes, all of these properties have been assigned one ERU and thus all are charged the same flat rate of $13.20 per month.

Non-Single-Family Residential

All other properties that are developed and not classified as Single-Family Residential are assessed a fee based on their ERU.

This category includes apartments and other multiple-dwelling residential unit properties, commercial and office buildings, public buildings and structures, industrial and manufacturing buildings, storage buildings and storage areas covered with impervious surfaces, parking lots, parks, recreation properties, public and private schools and universities, research facilities and stations, hospitals and convalescent centers, airports, water and wastewater treatment plants, and others.

To determine the stormwater fees for these properties, do the following:

  • Determine the impervious area in square feet. Add up all of the impervious surfaces such as buildings and parking lots.
  • Determine the property’s ERUs. Divide the total impervious area by 2,454 sq. ft.
  • Round up to find the Number of ERUs.
  • Multiply the Number of ERUs by the $13.32 rate. This is the monthly Stormwater Fee.


For a property with 100,000 sq. ft. of impervious area

Number of ERUs
= 100,000 sq. ft. / 2,454 sq. ft.
= 40.7 ERUs (round up)
41 ERUs

Stormwater Fee
= 41 x $13.32 per month
$546.12 per month