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1. What are stormwater utility fees?

Like gas, electricity, water, and sewage - stormwater runoff can be managed as a utility and billed as a fee. The fee is based on the concept that every property in a watershed contributes runoff and should support the operation, maintenance, and rehabilitation of the stormwater drainage system in the watershed. The amount of support is based on the amount of runoff the property contributes to the stormwater drainage system.

2. What is stormwater?

Stormwater is the runoff that results from precipitation. As this water flows over construction sites, farm fields, lawns, driveways, parking lots, and streets, it picks up sediment, nutrients, bacteria, metals, pesticides, and other pollutants. Unlike sanitary sewers that go to a treatment plant, most stormwater is discharged directly to local water bodies.

Increasing amounts of impervious surfaces in urban areas, such as rooftops, driveways, parking lots, and streets, decreases the ability of the water to soak into the ground, thus increasing the amount of stormwater. More stormwater places more demands on the city’s stormwater infrastructure.

3. What is an impervious surface?

An impervious surface is a hard surface that does not allow rain to absorb into the ground. Impervious surfaces increase stormwater runoff. Examples of impervious surfaces considered for the utility are roofs, paving (including gravel driveways), sidewalks internal to the site (not along the streets), sheds, paved patios, and pool decks. Surfaces not considered impervious: planting beds/landscaping features, the surface area of pools and decks (unless the area under the deck is paved).

To better understand how impervious surfaces are mapped and calculated view the impervious calculation document.

4. Who pays the fees?

Owners of all developed land in the City of Johnston would pay the stormwater utility fee. This includes residential properties, commercial properties, industrial properties, churches, and other nonprofit and governmental organizations. Undeveloped land is not charged stormwater utility fees because it does not have impervious surfaces.

5. How are stormwater utility fees charged?

The most fair and equitable basis for calculating stormwater charges is based upon the amount of a property's impervious area, which can be measured and has a direct and accepted relationship to the estimated amount of water that leaves a property as stormwater runoff. A property's impervious area is the most significant factor affecting both stormwater quality and quantity because stormwater cannot be absorbed by these surfaces and must be managed through some sort of stormwater system.

A unit of impervious surface area on an average single-family, residential property, or "equivalent residential unit" (ERU), is the quantity used for assessing the new stormwater charges. The size of one ERU was determined by averaging the impervious surface areas existing on all single-family properties around the city. The value of one ERU in the City of Johnston is set at 4,000 square feet of impervious area. Thus, the stormwater utility fee system is based on the total impervious surface area divided by 4,000 square feet; properties with greater than 4,000 square feet (1 ERU) of impervious surface are charged for more than one ERU.

For example: A property with 8,000 square feet of the total impervious surface would be billed for 2 ERUs. In all cases there are caps on the maximum number of ERUs that can be billed to the property, the cap for single-family residential properties is 4 ERUs and the cap for commercial, industrial, nonprofit, and all other properties is 40 ERUs.

6. How much are stormwater management fees?

The ordinance established a fee of $4.55 per equivalent residential unit (ERU) per month beginning July 1, 2012. The stormwater management fees are billed by the Johnston Water Utility and are made payable monthly at the same time payment for city water, sanitary sewer, and garbage are made.

7. How do I know how many equivalent residential units (ERUs) I’ll be billed?

If you would like to see how the impervious surface was calculated on your specific property you may contact city staff at 515-278-2344 or by email and an aerial map will be provided for your property showing the impervious surfaces.

8. How was the equivalent residential unit (ERU) rate determined for Johnston?

To determine the appropriate level of revenue needed to fund the utility, the city first analyzed the unmet needs of the stormwater utility system and developed a list of critical projects through the work completed with the Watershed Assessment and Stormwater Management Plan in 2009 and since that time other critical projects have been identified through the Capital Improvement Program; as noted on the list above.

Additionally, a small portion of the stormwater utility revenue annually will be used for operations and maintenance of the stormwater management system, with the intent of doing preventative maintenance to reduce the number of future capital improvement program projects. Using the costs and schedules of these projects and expenses, the city worked with Northland Securities, the city’s financial advisor, to determine the minimum fee necessary to fund those projects over a long term basis.

9. How will stormwater utility fees be used?

The stormwater management fees pay for

• Operation and maintenance costs of the stormwater management benefits and services and may include but are not limited to the provision of adequate systems of collection, conveyance, detention, treatment, and release of stormwater


• Reduction of hazard to property and life resulting from stormwater runoff and flooding


• Improvement in general health and welfare through reduction of undesirable stormwater conditions and flooding


• Improvement to the water quality in the stormwater and surface water system and its receiving waters

A list of capital improvement projects currently planned over the next 10 years that would be funded through the stormwater utility are available.