What Is Maryland’s Rain Tax and How Does It Work?

Maryland’s “rain tax” is the nickname for a stormwater remediation fee that certain local governments charge property owners based on how much impervious surface — rooftops, driveways, patios, parking lots — covers their land. The money funds projects that reduce polluted runoff flowing into the Chesapeake Bay and local waterways. Whether you pay anything, and how much, depends entirely on which jurisdiction your property sits in. Some counties bill a dedicated fee; others cover the same obligation out of their general budget and charge residents nothing extra.

The fee was created by House Bill 987 in 2012 and was mandatory for the state’s largest local governments. After political backlash, Senate Bill 863 passed in 2015 and made the fee optional, though every affected jurisdiction still has to run a watershed protection program and show the state it can pay for the required cleanup work.¹

Which Maryland Jurisdictions Charge the Fee

The underlying law applies to the ten Maryland jurisdictions that hold Phase I municipal stormwater permits under the federal Clean Water Act: Anne Arundel, Baltimore, Carroll, Charles, Frederick, Harford, Howard, Montgomery, and Prince George’s counties, plus Baltimore City.² If your property is anywhere else in Maryland, this fee doesn’t reach you.

Within those ten, the picture splits. Baltimore City, Anne Arundel County, Howard County, and Montgomery County kept active dedicated fees after the 2015 change. Montgomery operates its charge under a separate section of state law and calls it the Water Quality Protection Charge, but the mechanics are the same.³ Carroll County never imposed one, choosing instead to earmark general fund revenue each year.⁴ Frederick County charges a stormwater remediation fee of one cent per year per property — a protest measure left on the books.⁵

Call your county’s department of public works or environmental protection office if you aren’t sure what your jurisdiction does. The answer is specific to where you live, and it changes with local budget decisions.

How the Fee Is Calculated

Where a fee exists, the amount is tied to the impervious surface on your property. Every square foot of roof, driveway, sidewalk, patio, or parking lot where rainwater can’t soak into the ground counts. More hard surface means more runoff, which means a bigger bill.

Most jurisdictions measure in Equivalent Residential Units, or ERUs. One ERU is the average impervious surface area on a typical single-family lot in that area. In Montgomery County, one ERU equals 2,406 square feet.⁶ A single-family home is usually billed at one ERU. Commercial and multi-family properties get their total impervious surface measured and divided by the ERU value, so a commercial lot with 12,000 square feet of hard surface in a county using a 2,400-square-foot ERU would be billed for five ERUs.⁷

Measurements come from Geographic Information Systems and aerial imagery, not on-site inspections. That’s generally accurate, but it isn’t updated in real time. If you tore out a driveway last year, the mapping may still show it as impervious.

What a Typical Bill Looks Like

Rates vary by jurisdiction and by year. Montgomery County charges $147.00 per ERU for the fiscal year running July 2025 through June 2026.⁶ Baltimore City bills monthly alongside water and sewer; the most recently published rate is $7.20 per ERU per month, which comes to roughly $86 per year for a typical single-family home.⁸

Commercial sites can face much larger bills. A shopping center or warehouse billed for ten or fifteen ERUs will see annual charges in the four-figure range. Industrial complexes and big-box retail sit at the top end.

How the charge reaches you also depends on your jurisdiction. Some counties add it as a line item on the annual property tax bill. Others, like Baltimore City, bundle it into monthly water and sewer invoices. Either way, it’s accounted for separately from your property taxes.

Credits and Exemptions That Lower the Bill

Every jurisdiction that charges a stormwater fee also runs a credit program. The principle is straightforward: if you reduce the volume of runoff leaving your property, your bill drops. Qualifying improvements usually include rain barrels or cisterns that capture roof runoff, rain gardens that let water soak in naturally, permeable pavement that replaces solid concrete or asphalt, and green roofs planted to absorb rainfall before it runs off.

Credit caps vary. Some counties limit reductions to roughly 25% to 50% of the fee; others allow up to 100% if your on-site stormwater management is extensive enough. You apply through your local public works or environmental protection office, and you have to keep the installations in working order. Montgomery County inspects private stormwater facilities at least every three years, and a credit can be revoked if the feature falls into disrepair.⁹

Hardship exemptions exist in some jurisdictions for low-income homeowners. Eligibility is often linked to programs like the Maryland Homeowners’ Property Tax Credit, which is open to households with combined gross income under $60,000.¹⁰ Nonprofits and religious institutions may qualify for reduced rates or waivers depending on the local ordinance. None of these are automatic. You have to apply and document eligibility.

Disputing an Incorrect Assessment

If the impervious surface on your bill looks wrong, you can challenge it. The process is local, but Baltimore City’s rules are a reasonable model. A property owner first contacts the Department of Public Works to request a review. If customer service can’t resolve the issue, you have 30 days from receiving a bill you believe is incorrect to file a written appeal with your account number, the basis for the dispute, and supporting evidence such as an engineering survey or proof of a demolished structure.¹¹

Disputes are most worth filing when you’ve recently changed something the aerial imagery hasn’t picked up. Keep before-and-after photos, contractor invoices, and any as-built drawings. Those documents are what settle the question.

What Happens If You Don’t Pay

Unpaid stormwater fees don’t just sit on the books. In Maryland, unpaid property taxes and related local charges become a lien on the property from the day they come due, and state law requires each county’s tax collector to sell those liens at public auction.¹² A buyer at auction gets a tax lien certificate. If the homeowner doesn’t pay off the debt within a limited window, the certificate holder can move to foreclose.

That’s the worst case, and it isn’t instant. But even a smaller unpaid balance accrues interest and will surface in any title search, which means problems when you try to sell or refinance. Frederick County’s code is explicit on this point: its one-cent stormwater fee remains a lien on the property until paid and can be collected through tax sale if delinquent.⁵ If a penny-a-year fee can trigger lien procedures, a four-figure commercial bill certainly can.

Where the Money Goes

Stormwater fee revenue is walled off from the general fund. State law requires every affected jurisdiction to maintain a Local Watershed Protection and Restoration Fund, and fee revenue must be deposited there.³ The fund pays for stream restoration, detention pond maintenance, drainage upgrades, and other infrastructure that filters or controls runoff before it reaches local waterways. The Maryland Department of the Environment reviews each jurisdiction’s financial assurance plan every two years to confirm the program is funded and the work is getting done.¹³

1
Maryland General Assembly. SB 863 – Watershed Protection and Restoration Programs – Revisions
2
Maryland Department of the Environment. Maryland NPDES Municipal Stormwater Permits – Phase I and II Jurisdictions
3
Maryland General Assembly. Maryland Code Environment Section 4-202.1 – Watershed Protection and Restoration Program
4
Carroll County Government. Watershed Protection and Restoration Program
5
Amlegal. Frederick County Code Section 1-15.2-11.3 – Stormwater Remediation Fee
6
Montgomery County, Maryland. Rate and Charge Calculation – Water Quality Protection Charge
7
Montgomery County, Maryland. Multi-Family and Non-Residential Properties – Water Quality Protection Charge
8
City of Baltimore. FY 2023-2025 Water/Sewer/Stormwater Rates
9
Montgomery County, MD. Private Property – Stormwater Management
10
Maryland Department of Assessments and Taxation. Homeowners Property Tax Credit Program
11
City of Baltimore. Stormwater Remediation Fee Regulations
12
Maryland Department of Assessments and Taxation. Office of the State Tax Sale Ombudsman
13
Maryland Department of the Environment. WPRP Financial Assurance Plans