Sewer Overflow FAQs

What are CSOs and SSOs?

Combined Sewer Overflows (CSOs) are discharges of wastewater and stormwater from the combined sewer system that serves the downtown and surrounding areas. Sanitary Sewer Overflows (SSOs) are discharges of wastewater from the sanitary sewer system. Sewer overflows can occur at various discharge points along waterways when volume temporarily exceeds capacity, typically during wet weather.

Why do overflows exist?

Many years ago, prior to the existence of an Environmental Protection Agency (EPA) or Clean Water Act, it was common design for such relief points to exist in a sewer system in order to prevent backups into homes during wet weather and major rain events.

Where are the overflow points located?

Discharge locations are along the Olentangy River from Worthington to First Avenue, on the Scioto River from around Neil Avenue to S.R. 104, and on Alum Creek from Main Street to I-70. The locations are marked with signage. View Overflow Map.

Are overflows an issue in other U.S. cities?

Yes. Solving wet-weather issues is the biggest challenge facing most sewer districts today.

What is the City of Columbus doing about overflows?

The Department of Public Utilities developed a Wet Weather Management Plan in 2005, identifying an estimated $2.5 billion in capital improvement projects over the next 40 years. Sewer improvement projects are underway. Please see the Project Clean Rivers page and Blueprint Columbus for more information.

How will these projects affect sewer rates?

Sanitary sewer rates are expected to continue to rise in order to fund the improvements. An affordability analysis was conducted to ascertain the community's ability to pay for the projects. Revenue needs are reviewed annually.

How are sewer improvements financed?

Unless federal funding becomes available, sewer improvements will be financed through customer sewer rate revenue and by low-interest loan programs such as the Water Pollution Control Loan Fund through the Ohio EPA.

How will central Ohio residents benefit?

Anything that improves our environment and water quality benefits the entire community. Solving wet weather sewer issues will also reduce sewer backups into basements.

How many overflow points are in Columbus?

There are 33 SSO and 19 CSO discharge points owned by Columbus that can potentially overflow. Additional locations in the Columbus area are owned by other municipalities, one of which are maintained by Columbus under contract.

How often do they overflow?

The frequency and volume depend on the amount of rainfall and other factors. View discharge information or the previous year's annual report(PDF, 8MB) submitted to the Ohio EPA.

If I see an overflow warning sign, is it safe to swim near it?

No. First, be aware that swimming in local waters is prohibited by Columbus City Code and is considered a dangerous drowning risk in some locations due to low-head dams and utility crossings. To avoid possible negative health effects, always avoid water contact (including activities such as boating, wading, fishing and swimming) near a sewer overflow location, especially following periods of heavy rain. For more information, view reports from the U.S. EPA on the health and human impacts of CSOs and SSOs.

Can residents help prevent overflows?

Yes. Check your downspouts and foundation drains to make sure they are not connected to the sanitary sewer. These outdated connections, common in homes built prior to 1963, add excess water to the system during rain events. For a brochure on how to disconnect downspouts, please call (614) 645-2926.

Disposing of grease properly is also important as grease can block city and homeowner pipes, causing overflows and backups. Do not pour grease into sinks and drains. Place grease in the trash after it cools in a sealed container such as a coffee can. Also, make needed repairs on your home sewer line to prevent excess water from entering the system through cracks (often caused by tree roots).

Should residents report a suspected sewer overflow or basement backup?

Yes. Please report any suspected overflow or basement backup in Columbus immediately to the city's 24-hour Sewer Maintenance Operations Center at (614) 645-7102. This is also the first step to determine eligibility for the Project Dry Basement backflow prevention program for single and two-family homes in Columbus. Note, you may also call 311, or (614) 645-3111 for all non-emergency City services.

For questions, please email us at or call (614) 645-7175.