About Our Sewer and Stormwater System

Portland’s sewer and stormwater system includes pipes, pump stations, and treatment plants. It also includes green street planters, rain gardens, and trees. Together, this “grey” and “green” infrastructure helps us manage sewage and stormwater to protect people, property, and our environment.
On this page

Fast Facts

  • The system includes more than 2,500 miles of pipes, nearly 100 pump stations, and two treatment plants.  

  • About one-third of those pipes are more than 80 years old. Learn about construction projects to repair and upgrade aging pipes.  

  • The system serves more than 600,000 customers every hour of every day. This includes residents, businesses, industries, and visitors.   

  • Stormwater refers to rain that washes over hard surfaces like streets, sidewalks, and the roofs of buildings. Portland’s green infrastructure captures and filters about 2.3 billion gallons of stormwater each year. Learn more about how we manage stormwater in Portland.

  • With an inside diameter of 22 feet, the largest sewer pipe in Portland’s sewer system is the East Side Big Pipe, which captures combined sewage and stormwater to help prevent overflows to the Willamette River. The smallest pipes in the system are just 6 inches in diameter. Learn more about the Big Pipe Project.  

What’s the Difference Between Combined and Separated Sewers? 

Back in the 1860s when Portland started building its sewer and stormwater system, it was common practice to build combined sewers. These are sewers that carry both sewage and stormwater in the same pipe. Many of Portland’s older neighborhoods have a combined system.  

Diagram shows a house sewer lateral and a street storm drain flowing into the same sewer main, labeled combined sewer..

In a separated system, sewage and stormwater are collected and carried by two separate pipes. Sewage goes directly to the treatment plant, while stormwater can take a few different routes. Some stormwater gets piped to the treatment plant, some flows directly to a local creek or stream, and some is held until it can soak into the ground close to where the rain fell either through green infrastructure or other method.  

Diagram shows sewerp lateral from house flowing into sewer main and storm drain flowing into separate pipe, labeled stormwater

Your Sewer Lateral Connects Your Home or Business 

Nearly all of Portland is connected to the sewer system. Your home or business has a “lateral,” which is the pipe that connects your building to the sewer. The property owner takes care of the lateral, which in most parts of the city runs from the building to the curb. The City takes care of the “branch,” which is the portion of the pipe that typically runs from the curb to the main sewer line in the street.   

Diagram shows a street and house with a pipe, labeled, sewer lateral connecting the house to the public sewer main in the street. Diagram shows city maintains the part of the pipe from the main to the curb. The remainder is labeled as property owner maintains.

Current City rules require every building to have its own direct connection to the main line. If your property does not, then it’s considered “nonconforming.” You can learn more about nonconforming sewer connections and how to correct them.  

Your lateral is your connection to the sewer system, so it’s important to keep it clear of things that could cause a blockage. A blockage could result in a sewer backup into your home or business, which can be unhealthy for you and costly to clean up. Learn about what you should and should not flush to help protect your lateral. 

Gravity and Pumps 

Sewage, which is 99 percent water, flows downhill. Gravity is the main force that moves sewage through pipes. In places where it’s too flat or sewage needs to go uphill, pump stations push the sewage up so that gravity can take over again.  

Portland has nearly 100 pump stations with specialized pipes that can handle the force of sewage being pushed through them and the equipment to help control odor and protect the pumps. Operators at the Columbia Boulevard Wastewater Treatment Plant monitor the pump stations remotely and can quickly respond to emergencies like power outages or pump blockages. The Swan Island CSO Pump Station is the largest in the city. It’s so large that the Portland Building could fit inside its underground wet well.  

Big Pipes and the Swan Island CSO Pump Station 

In 2011, Portland completed the Big Pipe Project. When it rains, these pipes collect the sewage and stormwater flowing in from all the smaller pipes upstream in our neighborhoods. The Big Pipes can store up to 119 million gallons and allow plant operators to gradually pump that sewage to the treatment plant. This protects the treatment plant and has eliminated most combined sewer overflows to the Willamette River. 

Working with Nature: The Role of Green Infrastructure  

Green infrastructure brings nature-based solutions to the city. It includes green street planters, rain gardensecoroofs, trees, wetlands, and streams. Some are built and others are natural features of Portland. Plants and soil absorb and filter rain to help prevent water pollution, flooding, and more.  

For example, Portland has nearly 2,500 green street planters that slow and capture about 200 million gallons of stormwater each year. This helps prevent combined sewer overflows to the Willamette River or Columbia Slough and sewer backups into homes or the environment. The soil and plants in the green street planters filter pollutants out of the stormwater to help protect the water quality of our rivers and streams. Most green street planters let the water slowly soak into the ground to replenish groundwater. 

As climate change brings more intense rains to Portland, green infrastructure will be important for our sewer and stormwater system resiliency.  

Checking the Pulse of the System 

Even though lots of the sewer and stormwater system is underground, we know a lot about what happens inside of it thanks to our extensive flow and rain monitoring network. The Environmental Services field and data collection teams install and maintain hundreds of permanent monitoring stations and dozens of temporary sites each year to keep the data flowing. 

This consistent flow of data is a valuable tool used by our planners and engineers to help identify and prioritize projects to fix sewers, develop future plans, and assess stream flows. It’s like taking the pulse of the city’s sewer and stormwater system, so we can diagnose problems and target repairs to protect our community’s health and the water quality in our rivers and streams.