Where does that drain go?


At the University of Washington, water goes down three types of drains: sanitary sewer drains, storm drains and septic system drains. Depending on what the drain connects to, water and other material that go down the drain can end up in a sewage treatment plant that eventually drains to the Puget Sound, directly in Lake Washington or the Puget Sound, or in your septic tank. In short, only certain non-hazardous chemicals are allowed in the sanitary sewer, while only water is allowed in storm sewers. No chemicals or garbage are allowed in septic systems.

Sanitary sewer

Tacoma Central Wastewater Treatment Plant (courtesy of the City of Tacoma)(19K) Buildings in King County, including our campus buildings, are connected to the municipal sanitary sewer system of the City of Seattle and King County. Wastes flow in underground pipes from buildings to the West Point wastewater treatment plant. After treatment, the effluent is discharged into the Puget Sound.

At UW Tacoma and Friday Harbor, buildings are plumbed to city pipes which carry the wastewater to sewer treatment plants as well.

There are limits on the concentrations of pollutants that you put down the sanitary sewer drain. Hazardous waste is not allowed in the sanitary sewer. In addition, some wastes that don't designate as hazardous but are still harmful to pipes or workers, such as liquids with a pH of less than 5.5, sediment, and oils, fats and grease, are also not allowed in the sewer.

For details on what chemical wastes may be discharged to the sanitary sewer system in King County, click here. At UW Tacoma and Friday Harbor, limits are much more strict due to limited capacity of the wastewater treatment plant, and essentially no chemicals are allowed to be discharged to sanitary sewer.

If you have questions about what can be sewered, contact us at 206.685.3759 or email us at chmwaste@uw.edu.

Storm water system

Storm drainage systems are made of underground pipes that collect storm water runoff from streets, driveways and parking lots. At the Seattle campus, the pipes empty the untreated water directly into Lake Washington via the University Slough, near the Conibear Shellhouse, or down at Sakuma viewpoint near the Marine Studies building on south campus.

Only rain is allowed to go enter the storm water system. Chemicals, grease, detergents, food waste, garbage, oil leaking from your car - none of these is allowed.

UW Facilities Services labeled most of the storm drains on campus in 1999. The stenciling reads "DUMP NO WASTE - DRAINS TO LAKE". Their effort is part of a cooperative program with the City of Seattle to make people more aware that the storm drains route water, and anything else, directly to Lake Washington.

For more information, see our page about storm water runoff.

Combined sewer overflow

There are several locations on campus where we still have a few drains that go to combined sewer overflow systems. These systems are designed to drain to sanitary sewer except during exceptionally high rainfall, when some fraction of the water "overflows" to the storm water system and straight into the lake.

Septic systems

Some rural University-affiliated research stations (Pack Forest and others) rely on septic systems. A septic system is an underground tank in combination with a drain field. In a septic system, solid materials settle out in the tank and are gradually broken down by bacteria there. The liquid sewage flows out into the drain field where it is broken down further by soil bacteria.

Many hazardous chemicals can kill the bacterial action in the septic tank and drain field. These chemicals may also pass untreated through the septic system and seep into soil and groundwater. Therefore, do not flush or wash any toxic or non-biodegradable materials into septic systems, including toilet cleaners, bleach, and plastics.