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Stormwater Facility Credit

  • Permeable paving is a paving system which allows rainwater to percolate into the underlying soil.
  • Permeable paving is designed to slow the flow of stormwater.
  • Permeable paving can be used in walkways or driveways instead of soil, concrete or cement surfaces.
  • Porous cement can be used for sidewalks or driveways and allows water to drain to the underlying soil below.
  • Porous cement is an open-graded pavement system with small air pockets encased within the pavement.
  • Detention ponds are surfacewater basins that temporarily store rainfall to help prevent flooding.
  • They are typically designed to fill up during heavy rain events then drain in between storms.
  • Media filter systems are filtration systems that use sand or crushed granite to filter out pollutants from rainfall on impervious surfaces.
  • They can be designed as cartridges in a maintenance hole.
  • They can also be designed as cartridges in a vault underground.
  • Oil water separators are designed to separate oil and water. This allows the oil to stay in the system while the clean water discharges. There are two types of oil water separators; the baffle system, called American Petroleum Institute (API), and the coalescing plate system (CP) as shown here.
  • A detention system is a large pipe or vault that holds rainwater on the property and then allows water to flow slowly through a “flow control structure.”
  • The flow control structure has a small hole at the bottom of the pipe that meters the amount of water that can drain out of the detention system.
  • You should never enter a detention system without having had the proper training.
  • Bioretention systems are shallow depressions in the ground with designed soil mix and plants adapted to the local climate and soil conditions.
  • Bioretention systems can be designed to both detain and treat stormwater.
  • They can be used in common landscaped areas at business or residential properties.
  • They are intended to be used in small areas, with no one system larger than 800 square feet of bottom area.
  • They can be designed to take rainwater from rooftops, driveways or parking areas.
  • Green roofs are living vegetation systems installed on top of buildings to slow the flow of stormwater via soil storage, evaporation and transpiration. Green roofs consist of several layers of material to achieve the desired vegetative cover and drainage requirement.

If your property has a stormwater system, you may be eligible to save money on your annual drainage fee.

SPU developed the Stormwater Facility Credit Program to recognize privately-owned systems that reduce stormwater flow and/or provide water quality treatment, which help lessen the impact to the City's stormwater system, creeks, lakes, or Puget Sound. View the Stormwater Facility Credit Program Flyer (pdf).

If your property has a fully functioning, well-maintained stormwater system, you may qualify for a credit on your drainage bills. If you live in a single family home you may want to consider the Rainwise program for your property.

  • The impervious surfaces on a parcel are the hard cement or concrete surfaces that do not absorb rainfall during a rain event.
  • Stormwater flows off these surfaces into nearby catch basins, then into the property's stormwater structure before discharging into the City stormwater system.
  • Such surfaces include parking lots, driveways or parking garage entrances and exits.
  • Another type of impervious surface is roof top areas of buildings.
  • Rainfall drains off the roof into downspouts on the building and then into nearby catch basins or into the property's stormwater structures.
  • Walkways, stairs and areas outside doorways are other areas where impervious surfaces can be found.
  • Cement and/or concrete areas outside buildings are another type of impervious surface that can drain into the stormwater system.
  • Catch basins located on walkways can also drain into the stormwater systems on the property.
  • Stairs are another impervious surface type.

What are stormwater systems?

Stormwater systems are structures such as vaults, rain gardens, permeable pavements and infiltration systems that provide water quality treatment and/or slow down stormwater flow from impervious surfaces like rooftops, driveways or walkways.

Maintenance requirements

As the owner of a stormwater system, you are responsible for ensuring that the system is operating properly in accordance to the Seattle Stormwater code. Seattle Public Utilities (SPU) may conduct on-site inspections to verify that your facility is functioning and maintained in order for you to receive or continue to receive credit.

Learn more about:

Single family home

Typically, single family homes do not have stormwater systems that qualify for the Stormwater Facility Credit program. But you can still help improve water quality by installing green stormwater infrastructures. For information and technical assistance in installing green stormwater infrastructures on your property visit the Rainwise program.

To learn more about the Stormwater Facility Credit Program, visit our Frequently Asked Questions (FAQ) and How to Apply sections.

Related links

Stormwater Facility Maintenance Requirements
Rainwise Program
Green Stormwater Infrastructure
Stormwater Code