WQPC Rates & Calculation


The Water Quality Protection Charge is calculated based on how much of your property is impervious (does not allow rain to be absorbed into the ground). Properties with small buildings and little development pay less than properties with a lot of developed land.


How Was the Amount of Impervious Surface on My Property Determined?

Impervious surface data was gathered from imagery through geographic information systems (GIS) available from Montgomery County and the Maryland-National Capital Park and Planning Commission. Impervious surface area is calculated by totaling the square footage of any surface area that doesn’t allow for rain water to be absorbed.

The impervious surface area for your property is the total of:

  • Building area
  • Patio area
  • Attached or detached garage building area
  • Walkways
  • Driveway surface area
  • Basketball/tennis courts surface area
  • Private parking lots
  • Other paved areas with concrete or asphalt


Not included in the total:

  • Pools (Patios and paved areas around the pool are included)
  • Wooden decks
  • Front porches
  • Public sidewalks
  • Agricultural business buildings, such as barns or silos
  • Agricultural driveways
View an aerial of your property to see what was included in your WQPC. 


Payment Process

The Water Quality Protection Charge is assessed along with the annual property tax bill on July 1st each year. Payment process and schedules follows the rules and regulations of the Division of Treasury.

Image of a backyard in bloom. Interest on the overdue payment accrues according to the same schedule and at the same rate charged for delinquent real property taxes until the owner has remitted the outstanding payment and interest. An unpaid WQPC is subject to all penalties and remedies that apply to unpaid real property taxes. If the unpaid charge becomes a lien against the property, the lien has the same priority as a lien imposed for nonpayment of real property taxes.

  • Believe your WQPC has been assigned or calculated incorrectly?
  • Are you facing financial limitations that would prevent full payment of the WQPC? 
  • Do you own multiple properties and want them to be calculated as one contiguous unit?
Choose your property type from the list below to find out how to appeal your charge or receive a hardship exemption:



Basis for the Charge

Before calculating how much each property owner was charged, the County first determined how much impervious surface is on a typical property in Montgomery County. This number is called the  Equivalent Residential Unit (ERU). Property owners are charged based on how much more or less impervious space they have compared to the ERU.

Each tax year the County Council sets how much each ERU will cost. This number is called the Rate. For this tax year (2020),  the Rate is $119.50.

1 ERU = 2,406 square feet = $119.50

The exact amount of each property's charge is based on two factors:

  • The amount of impervious surface area on the property

  • The type of property owner


Choose your property type below to see how your charge was calculated: