By Joel R.
A big-box store and a corner coffee shop used to pay Mason City the same flat amount to handle the rain running off their roofs and parking lots: about $7 a month. Industrial properties paid about $12. That ended with billings on or after January 1, 2025, when the city began charging commercial and industrial properties by how much hard surface they have.
The change came in Ordinance 24-10, which the City Council adopted on June 4, 2024. Minutes of the May 7, 2024, meeting record Finance Director Brent Hinson saying it was hard to argue that a large big-box store should pay $7 a month when it put far more cost on the system than that. Under the new structure, a business with no more than 4,500 square feet of hard surface pays $3.01 a month on the ordinance’s schedule. That is less than half the old flat charge.
What is a stormwater fee?
A stormwater fee, also called a stormwater utility fee, pays for the pipes, intakes, ditches and basins that carry rain and snowmelt away from streets and buildings. Rain that soaks into the soil mostly stays out of that system. Rain that lands on a roof, a driveway or a parking lot runs into it. That is why a property is charged for stormwater even though no meter measures it. The system is visible in projects like the planned Highway 122 West overhaul, which would replace storm sewer pipes and intakes along one of Mason City’s busiest commercial corridors, NorthIowaToday.com reported in August.
Iowa cities set their own fees. The Iowa Stormwater Education Partnership says rates generally run from $3 to $15 a month per billing unit, so Mason City’s $3.01 is at the low end. City staff modeled the new structure on Dubuque’s. The May 7 minutes record Hinson saying that, compared with other communities over 10,000, Mason City “was still far below the average for this charge.”
Who pays the stormwater fee, and how the bill is worked out
The charge comes on the monthly city utility bill, alongside water and sewer. The ordinance makes the owner and the occupant jointly liable for it, which matters to tenants.
The billing unit is the ERU, or equivalent residential unit. One ERU is 4,500 square feet of impervious area “or fraction thereof.” That covers roofs, patios, porches, driveways, sidewalks, asphalt and concrete pavement, gravel surfaces and athletic courts.
- Houses and duplexes pay one ERU.
- Apartment buildings pay one ERU for every three units or part of three.
- Commercial, industrial, institutional and government properties pay for their hard surface divided by 4,500, rounded up, with a minimum of one ERU. Churches, hospitals and mixed-use buildings with apartments are in this group. The ordinance exempts public streets, alleys, sidewalks, drainage facilities and “other City facilities.”
The ordinance set the monthly rate at $2.92 per ERU from July 1, 2024, $2.98 from July 1, 2025, and $3.01 from July 1, 2026, “until amended.” At $3.01, before any credit, the finance director’s examples work out to:
- 23,000 square feet of hard surface (commercial): 6 ERUs, about $18 a month.
- 205,000 square feet (commercial): 46 ERUs, about $138 a month.
- 472,000 square feet (a major industry): 105 ERUs, about $316 a month.
- The property with the most hard surface in the city: 220 ERUs, about $662 a month.
The city’s parcel-by-parcel list shows each property’s ERUs for fiscal 2025, figured at $2.92 and before credits. About four in five billed properties on it have six ERUs or fewer, which is under $20 a month at $3.01.
The finance director’s memo gave three reasons for the change: fairness, revenue for coming capital needs, and an incentive for owners to manage stormwater on their own sites. Staff projected about $686,000 a year after credits, against about $447,000 under the old flat rates.
Can you get a stormwater credit?
Yes, for a short list of practices. The city engineer can cut a nonresidential bill by up to 40% for stormwater practices the owner puts in place and maintains. Homes and apartment buildings can’t get credits, because the city could not verify practices such as a rain barrel, the policy says.
The adopted credit policy lists:
| Practice | Maximum credit |
| Maintaining catch basins | 10% |
| Maintaining culverts | 5% |
| Maintaining creeks or streams | 5% |
| Detention basin that holds peak runoff to pre-development levels | 10% |
| Detention basin that cuts peak runoff at least 20% below them (4% each for 2-, 10- and 100-year rains) | 12% |
| Iowa DNR industrial stormwater permit (NPDES General Permit No. 1 or 2) | 10% |
| Capital Improvement Program “debt relief,” in rare cases | 26% |
Credits can be combined up to the 40% cap. There is no application fee, and an approved credit starts with the next bill. Most credits need engineering calculations, and the policy says a registered professional engineer may have to prepare some of them. A credit lasts one year, and then the owner re-applies.
The memo notes that many businesses already have detention or retention, which the city requires in new developments. The list has no credit for lawns, regrading or replacing pavement with grass. The application form mentions an “infiltration credit” that the policy does not define or value; the Engineering Department can say what it covers.
The other lever is the hard-surface figure itself. An owner or occupant who disputes the city’s calculation can appeal it to the city engineer. A granted appeal changes the charge from the next bill and may reach back up to three billing cycles. The ordinance does not say how the figure is updated after pavement comes out, so an owner who removes some should ask. Because ERUs round up in 4,500-square-foot blocks, a small change may not move the bill. Each full block removed is worth about $3 a month.
What the fee doesn’t fix
The fee pays for the city’s system. It does nothing about water trouble on the lot itself. Runoff ponds at entrances and refreezes on walks; Mason City averages about 90 days a year when the temperature crosses the freezing mark. It undercuts pavement edges, washes soil onto sidewalks and finds its way into basements.
This fall showed how much can arrive at once. Iowa had its fourth-wettest September on record, averaging 7.83 inches statewide, NorthIowaToday.com reported, citing the Iowa Department of Natural Resources. In a normal year, Mason City gets about nine days with an inch or more of precipitation, most of them between April and October.
Start with grading and drainage
I grade yards and lay sod in Kitchener-Waterloo, Ontario. Winters there are a little milder than North Iowa’s, but the freeze-thaw cycles and the Kentucky bluegrass are much the same. Most of the drainage problems I see can be found with a tape measure.
Check the slope at the building. According to the city’s website, Mason City reviews permits filed since January 1, 2026, under the 2024 International Building Code. That code requires the ground beside a new building’s foundation to fall away at 5% for at least 10 feet, with exceptions where lot lines, obstructions or soil conditions get in the way. A 5% slope is a 6-inch drop over 10 feet, the same figure the residential code uses for houses.
To check yours, run a string from a stake at the wall to a stake 10 feet out. Level it with a line level, and measure from the string down to the ground at each stake. The difference is the drop.
For a new building, that slope is a code minimum. On an older lot, walks, patios, lot lines and the neighbor’s yard all limit how much fall you can build, so treat it as the target. My company’s website has a step-by-step guide to grading a lawn so water drains away from the building. It is written for Ontario homes, but the measuring works the same way.
Fix bare, packed strips. The Iowa DNR’s stormwater manual names grading and compaction as the primary reasons development increases runoff. It says soils that have lost their organic matter to farming, development or topsoil stripping have lost 60% to 80% or more of their ability to absorb rainfall. In my experience, the worn strip along a parking lot or a delivery path behaves almost like pavement. Loosening it, adding compost or topsoil and getting turf growing again helps it soak water up.
None of this will lower the stormwater charge by itself. Managing stormwater runoff on your own lot keeps water away from doors, walks and walls.
What to ask
Walk the lot during the next heavy rain or the spring melt, and mark where water stands and which way it runs. Then take your questions to the city.
For the city’s Engineering Department (641-421-3605; billing questions go to Mason City Public Utilities, 641-421-3610):
- How many ERUs am I billed for, and how was my hard surface measured?
- Does anything on my site qualify for a credit, and what does the infiltration credit cover?
- When does my credit, if I have one, come up for renewal?
For a contractor:
- Where will the water go after the work, and will any of it reach a neighbor’s lot?
- What slope will the ground have for the first 10 feet from the building?