Understanding Your Drainage Bill

About the Bill

Where is my drainage bill?

Drainage fees do not appear on your utility bill. The City uses King County as its billing agent for the drainage fee. The drainage fee is shown on King County property tax statements as Surface Water Management (SWM) or Drainage. You can view your drainage fee by entering your property tax ID in the King County Property Tax Information System. If your mortgage company pays your property tax bill, they will include payment for drainage services which is factored into your escrow fees. Drainage charges are assessed on an annual basis.

Where do I find the Property Tax Account number on my property tax statement?

The property tax account number is in the upper left corner of your King County Real Estate Tax Statement. Also, you can call the King County Assessor's office at (206) 296-7300, and they will give it to you.

Who must pay a drainage fee in Seattle?

The City charges a drainage fee on all properties in the City, with the exception of the exempt properties noted in the Exemption section on this page. Seattle's drainage system is a City-wide utility. All properties contribute to the problem of water runoff and benefit from the drainage system through flood control and improvement of water quality.

Who is responsible for paying the fee?

The property owner of record (per King County Assessor records) is responsible for paying drainage charges. The bill will be included on the property tax statement and sent to the person to whom the property tax statement goes. For example, a shopping center with six separate businesses and only one property owner will receive one bill for drainage on the property owner's property tax statement.

I own a condominium. Is the drainage bill sent to me or to the Condo Association? How is my portion of the fee of the condominium complex calculated?

Condominium complex bills will be divided equally among the building units and are sent separately to the individual condominium unit owners listed on the King County Assessor's Real Property File. For example, if there are 10 units in a condominium complex, each unit will receive a bill for one-tenth of the total complex bill.

I own more than one piece of property. Will all charges be consolidated or will I get multiple bills?

The drainage charges will appear on each of your property tax statements. Thus, the drainage charges will be billed in the same manner as your property taxes.

I own a rental property. Will I still be billed if it is vacant and all utilities are shut-off?

Yes. The property contributes runoff and benefits from the drainage system whether or not anyone is living on the property.


Drain cleaning process is shown
SPU maintains, repairs, and replaces pipes and pumps. (Enlarge repair image)

Bill Calculation

How is my drainage bill calculated?

The method for calculating your bill depends on the type of property you own.

  • Single family and duplex properties smaller than 10,000 square feet are assigned to drainage rate categories based on the size of the parcel. All properties in a given rate category pay the same flat rate. View the current rate schedule for small residential and duplex property rates.
  • All other properties, including single family and duplex properties 10,000 square feet and larger, are assigned to rate categories based on how much impervious surface is contained on the parcel. Each rate category is assigned a rate which is multiplied by the parcel area (in 1,000s of square feet) to calculate the total charge, or bill.

How did Seattle Public Utilities (SPU) determine what the rate categories are?

SPU's drainage rate categories group parcels with similar property characteristics which will, in turn, contribute similar amounts of stormwater runoff. SPU estimates the fraction of rainfall that becomes "runoff" from a parcel using standard runoff coefficients utilized in hydrological modeling. These runoff coefficients vary depending on how pervious (permeable) a surface is. More stormwater will run off of hard or impervious surfaces while pervious or permeable surfaces will absorb more water.

The amount of stormwater that will run off of a property depends on the type of surface covering the property and its size. The SPU rate categories incorporate both of these factors in the development of their respective rates. The fee structure for some rate categories relies on category averages for surface type while the structure for other categories is based on parcel specific surface type information and size. However, the assumptions regarding how much stormwater will flow off of a given surface are consistent across all rate categories, regardless of fee structure.

Small residential customers with billable areas less than 10,000 square feet are charged a flat rate based on the surface type profile for a typical customer in the specified rate category. These properties, which account for approximately 93% of all single family and duplex parcels, are fairly homogeneous in terms of surface cover, which makes property size the key determinant of parcel stormwater flow contribution. Small residential customers are assigned to one of four size-based categories, each representing a range of total area (e.g., 3,000 to 4,999 square feet). SPU used sample data collected city-wide from aerial photographs for small residential parcels to estimate the typical surface types for each parcel size range. This surface type information combined with the parcel sizes within each category was used to develop the respective flat rate by category.

Drainage bills for large single family and duplex parcels 10,000 square feet or greater ("large residential") and commercial parcels (all sizes) are calculated by multiplying a rate per 1,000 square feet of billable parcel area by the parcel's actual billable area. There is too much variation between these properties in terms of parcel size and surface characteristics to be fairly captured by a flat rate structure like that applied to small residential customers. SPU has five impervious surface-based rate categories. Each category represents a range of impervious surface (e.g., 66-85 percent impervious). In addition, low impact rates are available for commercial and large residential parcels which contain significant amounts of highly pervious (absorbent) area and which are composed of no more than 65% impervious area.

What is impervious surface?

Impervious surface is any hard or impermeable surface such as blacktop, rooftops, parking lots, patios, hardpan, and hard packed athletic fields. This type of surface absorbs much less rainwater than pervious surfaces covered with grass, trees, or other vegetation.

How did you determine the percent of impervious surface area on my property?

SPU uses surface type mapping data collected from aerial photos to determine the percent of impervious area on each property.

What parcels may qualify for low impact drainage rates?

Low impact rates apply to large residential and commercial parcels with significant amounts of highly pervious surface, such as forested land, unmanaged vegetated areas such as pasturelands and meadows and athletic fields designed with specific drainage characteristics. This highly pervious surface must cover a continuous area of at least one-half an acre, although this coverage may span more than one parcel. Low impact rates are available for the Undeveloped (0-15 percent impervious), Light (16-35 percent impervious) and Medium (36-65 percent impervious) rate categories.

Why are low impact rates lower than rates for other properties with the same percentage of impervious surface?

Parcels containing large amounts of highly pervious area will generate significantly less stormwater run-off than parcels with similar amounts of impervious surface but whose pervious area is less absorbent (e.g. a managed lawn).

How do I know if my parcel contains enough highly pervious surfaces to qualify for a low impact rate?

The total estimated stormwater runoff for a parcel is calculated based on specific stormwater runoff factors for each surface type. If the total run-off for a given property falls below specific thresholds for each rate category, the parcel will be billed the low impact rate. SPU customer service can verify if your property meets a low impact threshold if the parcel area, impervious area, and highly pervious area are known.

To be considered for these rates, the area which is considered highly pervious must span an area of at least one-half an acre. This area may include continuous coverage on an adjacent parcel or parcels. Secondly, the area must be in a natural, unmanaged state. Golf courses, landscaped parks or lawns, and other developed pervious areas do not qualify as highly pervious.

An athletic field meeting specific design requirements can be considered for the low impact rate. To apply for this reduced rate classification contact SPUDrainageBilling@seattle.gov and request an application.

Why do small residential properties pay a flat rate and no one else does?

Drainage rates are structured so that each property is assigned a cost which is proportionate to its impact on the drainage system. Properties assigned to small residential rate classes are relatively homogenous both in terms of size (limited square feet ranges for each rate category) and the type/size of structures on their properties. Therefore, using actual impervious surface information for a sampling of these properties allows us to develop a good estimate of stormwater runoff from properties in a narrow lot size band. In addition, collecting and maintaining property data for a sample of these properties, rather than the entire population, holds down administrative costs as these properties account for 74% of all parcels and 93% of residential properties.

There is a much greater variance in lot size and property composition on residential properties 10,000 square feet and greater. Likewise, non-residential properties vary considerably in terms of lot size and the type/amount of surface covering these parcels. Therefore, the fairest way to bill these properties is to use their actual lot size and percent impervious.

Is my drainage rate the same thing as my drainage bill?

That depends on the size and type of your property. For small residential and duplex properties smaller than 10,000 square feet, the drainage rate, which is a flat fee, is equal to the total drainage bill. For all other properties, the drainage rate for the assigned category must be multiplied by the lot area (in 1,000's of square feet) to calculate the total drainage bill.


Spill response team in action
Protecting local waterways from pollution is the highest priority. (Enlarge waterway image)


Who is exempt?

The following properties, or qualifying portions of properties, are exempt from payment of drainage charges:

  • submerged land,
  • houseboats,
  • piers,
  • City streets, State of Washington highways, and other streets that provide drainage services in the same manner as City streets,
  • islands that contain highly infiltrative pervious surface and less than ten percent impervious surface area,
  • riparian corridors that contain highly infiltrative pervious surface and meet certain qualification criteria
  • wetlands that meet certain qualification criteria

How did you determine which land is submerged?

Submerged land was identified using Geographic Information System data developed to describe the interface between land and water.

My property is partially submerged. Am I still required to pay a drainage fee?

Yes. However, your fee will be calculated on the unsubmerged portion of the property.

How are streets other than City streets qualified?

Streets are qualified through an application process. In order to qualify properties and streets must meet the guidelines outlined in the 2012 SPU Directors rule. For more information about qualifying streets please contact (206) 684-5948.

How are exempt islands and riparian corridors qualified?

SPU qualifies properties based on its analysis of both impervious and pervious surface billing data collected from aerial photos and other sources. Detailed qualification criteria for exemption of riparian corridors can be found in SPU Director's Rule FIN-211.2 (pdf). Property owners may request a review of their property's characteristics through the billing adjustment process discussed later in these FAQs if they believe their property meets the qualification criteria for these billing exemptions.

How are exempt wetlands qualified?

Property owners must submit an application and required supporting documentation to be considered for a wetlands exemption. To request an application packet, please contact Tasha Bassett at (206) 615-0550 or Tasha.bassett@seattle.gov. Detailed qualification criteria and administrative procedures can be found in SPU Director's Rule FIN-211.3 (pdf).


Sea Street Swale
We engineer solutions to protect local waterways from stormwater runoff. (Enlarge planting image)

Special Programs

Does SPU offer any credits or discounts?

Drainage bill discounts are available for property owners that help reduce the impact of stormwater on the City's system. SPU currently offers bill reductions to both natural areas whose characteristics enhance retention of stormwater runoff, as well as to engineered systems that provide stormwater flow control and/or provide water quality treatment for run-off from impervious area.

  • Low Impact Rates
    Discounts of 20 to 41 percent are applied to the rate for undeveloped natural areas of 0.5 acres or greater containing sufficient amounts qualifying "highly infiltrative" surface (i.e. forested areas, unmanaged grasslands, etc.). Certain athletic facilities with engineered designs that mimic the stormwater retention benefits of these large natural areas are also eligible for low impact rates.
  • Stormwater Facility Credit Program (SFCP)
    This program offers credits of up to 50 percent for privately-owned systems that slow down stormwater flow and/or provide water quality treatment for run-off from impervious areas, thus lessening the impact to the City's stormwater system, creeks, lakes or Puget Sound. Stormwater systems are structures such as vaults, rain gardens, permeable pavements and filtration systems. View qualification criteria, application procedures, and more about the Stormwater Facility Credit.
  • Rainwater Harvest Credit
    SPU offers a 10 percent discount for any new or remodeled commercial buildings that utilizes a rainwater harvesting system meeting credit requirements. Those systems that involve indoor uses of rainwater must be permitted by Seattle-King County Department of Health in order to qualify for the rate reduction. Systems must meet the applicable stormwater and drainage code requirements for the building and site. 

Will properties with on-site detentions systems be billed?

Yes, but they may qualify for a credit. View the Stormwater Facility Credit for more information.

Is there an adjustment for low-income, elderly, or handicapped people?

Yes. If you qualify for an adjustment on your sewer bill, you will automatically receive an additional adjustment for drainage. This adjustment will be included on your combined utility bill rather than on your drainage bill included on your property tax statement.


Bill Payments

Can I pay my drainage fee at the Community Service Centers?

No. The drainage charges are included on your property tax statement and must be paid with the property taxes.

Can I pay my drainage fee in two halves, just as with my property taxes?

Yes. The drainage charges can be paid in two halves just like the property taxes.

My property was sold after I paid my drainage fee. How do I get a refund for part of the year?

Since the drainage fee is included in the property tax bill, if a property is sold in the middle of the year any portion of the unused drainage fee is included in the escrow settlement process.

What happens if I don't pay my drainage fee?

Delinquency charges will be applied for delinquent drainage fees. If the drainage fee is not paid, a lien may be attached to the property.

Is the drainage fee deductible on my federal income tax?

No. This charge is a utility fee like water, sewer, or garbage charges.


Bill Adjustments

I feel my bill is incorrect, may I have it adjusted?

In order to be considered for an adjustment, the following criteria must be met:

  • Payment on the account must be current. Requests for adjustments on delinquent accounts will not be considered for review
  • Requests for adjustments must be received within 90 days from the billing date, requests received after that point will still be considered but will be applied to subsequent years only
  • Requests for adjustments must be made in writing
  • The burden of proof is on the applicant to show that an adjustment should be made

How do I request an adjustment?

Customers may request an adjustment by emailing their parcel number or parcel address to the SPU Drainage Billing Team: SPUDrainageBilling@seattle.gov.

What happens after the Utility reviews my property?

  • If the Utility grants an adjustment that reduces the charge for the current year, the customer will receive a revised bill and/or a refund of the amount overpaid.
  • If the Utility determines that an adjustment should be made which increases the charge due for the current year, the applicant will receive a revised bill that will be due within 45 days of the date of issue.
  • All customers will be notified of the Utility's decision.
  • All decisions of the Utility are final.

What number can I call if I still have questions?

Contact SPU Customer Service at (206) 684-3000.


Related Links

Payment Assistance Programs
King County Property Tax Information System


Public Utilities

Andrew Lee, General Manager and CEO
Address: 700 5th Avenue, Suite 4900, Seattle, WA, 98104
Mailing Address: PO Box 34018, Seattle, WA, 98124-5177
Phone: (206) 684-3000

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Seattle Public Utilities (SPU) is comprised of three major direct-service providing utilities: the Water Utility, the Drainage and Wastewater Utility, and the Solid Waste Utility.