Cary Town Council members spent part of Tuesday's meeting picking apart how the town might someday charge residents for stormwater service, floating a model that would size up driveways, rooftops and tennis courts instead of folding the cost quietly into everyone's taxes. No vote was taken, and no dollar figures were put on the table.
Right now, Cary pays for stormwater services out of its general fund, according to WRAL. Mayor Harold Weinbrecht told fellow council members that this setup is essentially a flat-rate system, and he was careful to note that any shift in billing method wouldn't necessarily mean residents pay more overall — just that the way the bill gets calculated would change.
The alternative under discussion is known as an Equivalent Residential Unit, or ERU, system, which calculates fees based on how much impervious surface sits on a property. Impervious surfaces — driveways, tennis courts and rooftops among them — stop rainwater from soaking into the ground, which can worsen flooding or property damage nearby, per the same report. One ERU represents the average impervious footprint of a typical single-family home in a given area; using an example where one ERU equals 3,000 square feet, a parcel with 6,000 square feet of hard surface would be billed for two ERUs.
Who Would Pay More, Who Might Pay Less
Corvias Infrastructure Solutions modeled different stormwater funding scenarios for the town, drawing on an analysis of more than 52,000 billable customers built from Cary's own GIS parcel data. Sri Vedachalam, the firm's managing director of advisory services, told council that Cary would be a good candidate for an ERU system and argued it could spread rate charges more systemically and more fairly to owners of smaller properties, the station's report notes.
Vedachalam pointed out that many places stick with flat fees simply because they're easier to administer, but that approach can mean a townhouse and an Amazon warehouse get charged the same amount under a flat-rate model. Council member Michelle Craig said residents with smaller homes and less paved or roofed surface could end up saving money under an ERU system compared with owners of very large homes.
Craig also raised a wrinkle that cuts against intuition: a two- or three-story home with 3,000 square feet of living space might actually have a smaller ERU footprint than a single-story ranch home with the same amount of living space, since the impervious surface a home sits on — not how much living space is stacked on top of it — is what the formula measures. She added that an ERU or hybrid ERU model would not charge residents of vertically stacked multi-family homes disproportionately more, according to the same account.
The Administrative Tradeoff
An ERU system requires more upfront calculation than a flat fee, but Cary's robust GIS resources already offer the data needed to crunch those numbers, per the report. Cary separates its water from its waste.
The conversation fits a broader pattern across the state. A survey covering 101 North Carolina stormwater utilities for fiscal year 2024 found that flat-fee structures remain predominant for residential customers, according to the UNC Environmental Finance Center. Tiered flat fees that vary by impervious surface are more common among single-family residential properties, while charging per ERU is the preferred method for nonresidential properties in that same survey. Roughly 30% of the surveyed utilities raised stormwater fees between fiscal years 2022 and 2024, with residential increases ranging from 8 cents to $14.43.
That survey also found the median monthly residential stormwater bill sat at $5 for properties with between 3,000 and 6,000 square feet of impervious surface, while nonresidential properties saw median bills of $15.61 at 10,000 square feet and $76.07 at 50,000 square feet. A separate Environmental Finance Center analysis argues that impervious-surface-based billing is theoretically the most equitable approach, since stormwater costs track with runoff, though calculating exact impervious area for every parcel can be administratively burdensome enough that many utilities simply charge residential customers a flat one-ERU fee instead. The same analysis notes tiered fee structures exist as a middle option between flat fees and strict per-ERU billing.
One study of Roanoke, Virginia, cited in that analysis found residential customers shouldered 2.4 times their equitable share of stormwater revenue under a flat fee charged by customer class, compared with 1.1 times their share under a per-ERU structure. North Carolina's enabling statute, found in Chapter 162A of the General Statutes, allows authorities to impose rates and fees for stormwater management programs, while a separate provision in Chapter 153A, Article 15 permits local governments to jointly run stormwater services even though only one unit may levy the fee within a shared service area.
For now, Cary's discussion remains conceptual. Tuesday's meeting produced no vote, no proposed rate schedule and no timeline for when — or whether — the town might formally adopt a new billing structure.
