Where a Columbus shower drains to, and what happens next

Water that goes down a shower drain in Columbus leaves the house through a private lateral, joins a public sewer in the street, and ends at one of two treatment plants that return it to the Scioto River south of downtown. Getting it there is one of the largest public works programs the city runs, and parts of that program reach onto private property. This page traces the route, separates a combined sewer from a separate one, dates the system from 1841 to the tunnel finishing this year, and sets out the rules a homeowner meets when a basement is involved. Every figure on it is the city's, Ohio EPA's, the federal EPA's or the code's own, and the two news reports it cites are named where they are used.

Last updated September 2026 · Figures are the city's, Ohio EPA's, US EPA's and the code's own, read September 2026 · No prices on this page; the Estimate Builder carries those · Part of the knowledge base

Where a Columbus shower drains to

The route is short and one way. Waste water leaves the house through a private lateral, joins a public sewer in the street, and travels through the city's collection system to one of two treatment plants, Jackson Pike or Southerly. Ohio EPA describes the arrangement the same way the city does. Both plants return the treated water to the Scioto River south of downtown.

The system does not serve Columbus alone. The city's 2024 annual report says the two plants serve Columbus and 26 contracting suburban communities. That count is not stable across the city's own pages, and two others published in the same season say 25 and 29, so the number here is the annual report's, with its year. The city's contract community list names Bexley, Dublin, Gahanna, Grove City, Hilliard, New Albany, Reynoldsburg, Upper Arlington, Whitehall and Worthington among others, along with several smaller villages and part of unincorporated Delaware County, and says Canal Winchester and Pickerington are not served. That list covers water contracts and sewer contracts together, though, and does not say which of the two services each community holds. The pipe between the house and the sewer in the street has a page of its own, on the lateral and the drains under the house.

Combined sewers, separate sewers, and which Columbus has which

A combined sewer carries sanitary waste water and street and roof runoff in one pipe. A separate system splits that into two pipes, a sanitary sewer for what leaves the house and a storm sewer for rain, and Columbus counts its mains in those three categories. Ohio EPA says it no longer permits the installation of combined sewers, though the agency gives no date for when that began.

The proportions are worth having. Columbus Water and Power reported maintaining 4,650 miles of city-owned sewers in 2024: 2,626 miles of sanitary sewer, 1,824 miles of storm sewer and 156 miles of combined sewer. Those are city-owned miles for calendar year 2024 and they do not include private laterals; the city maintains a further 43 miles of county-owned sewer under contract. The mileage moves as the city separates old sewers and builds new ones, which is why the year matters: Ohio EPA counted 2,782 miles of sanitary sewer and 167 miles of combined in its 2020 assessment.

Where those combined sewers are is the question this page cannot answer address by address. Ohio EPA describes the combined sewer system as the oldest part of the Columbus collection system. The city describes it as the system that serves the downtown and the surrounding areas. Neither publishes a boundary, a street list or a map legend saying in words how far it reaches, and no city or state document found for this page draws the line any more precisely than that.

The overflow points are published. In a large storm a combined sewer is built to let part of the untreated flow spill to the nearest waterway rather than back up into basements, which is what an overflow point is for. Columbus reports 19 combined sewer discharge points of its own that can overflow, along the Olentangy, the Scioto and Alum Creek, and it runs a public map of overflow locations and events.

Age is the other half of the story, and it is not theoretical. The Columbus Dispatch reported in May 2026 that a brick combined sewer the city built in 1900 had collapsed about thirty feet below German Village, closing streets; the city said the repair could take four to six weeks and that the sewer had last been inspected in 2012.

The system in one arc, from 1841 onward

The city's own milestone list dates the first sewer in Columbus to 1841, discharging untreated to the Scioto River. The same list says that by 1900, 144 miles of public sewer reached about 80 percent of the population; a separate entry for the same year describes the system as combined, discharging untreated into Alum Creek and the Scioto River.

The city says its first waste water treatment plant, the Improved Sewage Works, went into service in 1908, just south of where Jackson Pike crosses the Scioto. That first plant ran on septic tanks, then stone-filled sprinkling filters, then final settling tanks, and was designed for twenty million gallons a day. It should not be confused with the 1908 water purification works, which treated the drinking water and belongs to the page on where Columbus water comes from.

The city says the Jackson Pike plant was placed into service in 1937, on the site next to the 1908 works, using the activated sludge process. Its own milestone list stages that more carefully: construction began in 1934, the primary treatment portion was brought online in November 1937, and the activated sludge process was commissioned in 1938. The city's 2024 annual report gives the year as 1935. The in-service year printed here is 1937, because the milestone list dates that November startup precisely.

The city says the Southerly plant went into operation on August 14, 1967, and serves eastern Franklin County. Jackson Pike is rated for a design flow of 68 million gallons a day, a figure the city and Ohio EPA both publish. The city gives Southerly an average daily design flow of 114 million gallons a day. The two publishers do not agree on Jackson Pike's peak, so no peak figure appears on this page.

The consent orders, and the plan that came out of them

Columbus entered two consent orders with the state, in 2002 and 2004, over sewage overflows and basement backups. US EPA describes the pair as covering overflows from the sanitary sewers, basement backups and overflows from the combined sewers. The city's milestone list ties the 2002 agreement to sanitary sewer overflows and records a second order in 2004, so it is the pair that covers both kinds of overflow.

Columbus answered with a Wet Weather Management Plan submitted to Ohio EPA in 2005, which the city calls a forty-year plan. In 2012 the city began an integrated planning process to update that 2005 plan around cheaper and greener measures, and that process is where Blueprint Columbus came from, three years before the plan bearing that name existed. Ohio EPA approved the final Blueprint Columbus integrated plan in 2015 and wrote it into one of the plant permits.

The deep tunnels

Two of the largest pieces of the plan are holes in the ground. OARS, short for the Olentangy Scioto Interceptor Sewer Augmentation and Relief Sewer, runs about 23,300 feet, just under four and a half miles, at a finished diameter of twenty feet and roughly 170 feet below the surface. It intercepts wet weather overflows that used to empty into the Scioto and carries them to Jackson Pike and Southerly, and the city says it holds about sixty million gallons of combined sewage until it can be pumped out for treatment.

The city gives two dates for finishing it. Its 2017 annual report says that with construction complete, the OARS system was put into operation in July of that year. Its milestone list dates the completion to 2018, tied to the closure of the Whittier Street gates. Both are the city's own and may be describing two different steps, so this page prints both.

The Lower Olentangy Tunnel is the newer one: a twelve-foot diameter tunnel about 17,000 feet long, running from Tuttle Park north of the Ohio State campus south to the Arena District, where it meets OARS, and everything it collects goes to Jackson Pike. Ohio EPA and the city agree on its length and diameter but not on its depth: the city gives an average of 50 feet, Ohio EPA a range of generally 55 to 70 feet. WOSU Public Media reported that the tunnel's boring machine broke through at Tuttle Park on June 4, 2025. The city says construction began in early 2021 and is planned to finish in September 2026; Ohio EPA's 2020 assessment had expected completion by March 2026, against a consent order deadline of July 1, 2025.

Blueprint Columbus, and the part of it that happens at the house

Blueprint Columbus is the city's alternative to parts of the 2005 plan, approved by Ohio EPA in 2015. Its four pillars are lining private sewer laterals, redirecting roof water, installing sump pumps and building green infrastructure. Three of the four happen on private property, which is what makes this a homeowner subject. US EPA states the reason plainly: storm water and ground water enter the sanitary sewer system through cracks and improper connections, and that is what causes the overflows and the basement backups. A Blueprint sump pump sends ground water out to the street and the storm sewer, so that it stays out of the sanitary sewer. Why so much ground water finds its way in, the wet soil under most of the county, is on the page about what goes wrong in a Central Ohio house.

The city says Blueprint Columbus will reach 21 neighborhoods over thirty years, and its own frequently asked questions say that construction in a neighborhood generally runs eighteen to twenty-four months.

Columbus City Code 1145.88 says the costs of all corrective measures the city takes on private property are paid by the city. That applies inside areas the director has designated for the inflow and infiltration reduction program, not city-wide, and the code says the city may install a sump pump in a single family or duplex home only with the owner's written permission. The same code section makes the property owner responsible afterward for maintaining the lined lateral, the redirected downspouts and the sump pump; it adds that later repair or replacement is paid by the owner, and that any warranty transfers to the owner.

One measurement in the same chapter is worth carrying around. Under the code a downspout counts as indirectly connected to the foundation drain if it discharges within seven feet of the foundation, and it may be redirected to the street or at least seven feet out. That seven feet is what decides whether a downspout is treated as feeding the sanitary sewer, which is worth checking before anyone regrades or repaves beside the house.

For the lining itself the city says residents are asked to suspend water use for about four hours on the day, while the liner hardens, and that a newly lined lateral has a life expectancy of 50 years. The city's 2017 annual report counted 112 sump pumps installed and 27 downspouts redirected in the first Clintonville project area that year. Blueprint Columbus reports, in its own words, a 99 percent reduction in sanitary sewer overflows resulting from heavy rain events; the program names no baseline year and no area for that figure, so read it as the program's claim about its own finished work.

The rules a Columbus homeowner meets

Columbus City Code 1145.84 says no person shall connect roof, foundation area way, parking lot, roadway or other surface runoff or ground water drains to a sanitary sewer connected to the city's treatment works. It calls such connections illegal and subject to removal at the owner's expense. The same section allows storm water into a sewer specifically designed and designated as a storm sewer or a combined sewer, and asks that it go to the storm sewer where both are available. So the prohibition is about the sanitary sewer in particular, not about roof water everywhere, and the list it gives is a list of drains rather than of pumps.

Inside the house the rules are the plumbing code's. The Residential Code of Ohio incorporates the Ohio Plumbing Code for plumbing in buildings within its scope, with a short list of changes, so the drainage sections that govern a Central Ohio bathroom are the plumbing code's rather than the residential code's own. The Ohio Plumbing Code says storm water shall not be drained into sewers intended for sewage only.

Ohio rewrote the backwater valve rule, in a version of the sanitary drainage rule effective October 15, 2025. Under it a backwater valve is installed only where Ohio EPA or the local sewer purveyor requires one, and only for plumbing fixtures on a floor below the elevation of the next upstream manhole cover. The valve goes in the building drain or the horizontal branch serving those fixtures, not necessarily out at the lateral, and fixtures above that level are not to discharge through one at all, except in an existing building. Whether one is called for at a given address is a question for the sewer purveyor there, and Central Ohio is more than one jurisdiction.

The plumbing code also says a drain below the sewer that cannot be discharged to it by gravity flow must go into a tightly covered and vented sump and be lifted out automatically by a sewage pump or ejector. That is the rule behind the pit under a basement bathroom. In a building under the Residential Code of Ohio only a check valve is required on the pump's discharge piping, where other buildings need a check valve and a full open valve. Central Ohio's flood record, the dams built since and the maps that set flood zones are on the floods, dams, levees and floodwalls page.

For a house that has already had a backup, the city's Project Dry Basement, begun in July 2004, covers an approved backflow prevention device for single and two-family homes that have had sewer backups, and the city counted 1,814 installations through the end of 2024. The city says a backup should be reported to the Sewer Maintenance Operations Center, where it is reviewed for eligibility, or reported through an online wet basement questionnaire.

What all of this means for a basement bathroom

Most bathroom work in Central Ohio meets none of it, because a fixture above the sewer drains by gravity the way it always has. A basement bathroom is the exception, and two of the facts above turn into decisions on a floor plan. The covered, vented pit and its pump take floor space and add a step to the schedule. A backwater valve is not automatic and is not always allowed, since it depends on the fixture's level relative to the next upstream manhole cover and on what the sewer purveyor requires. In a Blueprint neighborhood, the four-hour water shutoff for lining is worth knowing about before a bathroom is booked.

The pipe itself, its material, its age and who looks after it, is the subject of the page on the lateral and the house drains. On this site, the page on tub-to-shower conversions covers what changes at the drain when a tub comes out, and the page on wet rooms covers the case where the whole bathroom floor drains.

Sources

Every figure, date and quotation on this page comes from one of these documents, read on the date given. Where two of them disagree, the page says so.

• City of Columbus, Columbus Water and Power, 2024 Annual Report, 2025; read September 2026.
• City of Columbus, Columbus Water and Power, Water and Sewer Contract Communities, undated; read September 2026.
• Ohio Environmental Protection Agency, Final Finding of No Significant Impact and Environmental Assessment, City of Columbus Lower Olentangy Tunnel, November 16, 2020; read September 2026.
• Ohio Environmental Protection Agency, Combined Sewer Overflow Control Program, undated; read September 2026.
• City of Columbus, Columbus Water and Power, Sewer Overflow FAQs, undated; read September 2026.
• The Columbus Dispatch, Brick sewer collapse under Columbus' German Village forces month-long closures, May 27, 2026; read September 2026.
• City of Columbus, Historical Milestones for Wastewater Treatment in Columbus, undated; read September 2026.
• United States Environmental Protection Agency, Integrated Planning in Action: Integrated Plan and 2015 WWMP Update Report, Columbus, Ohio (EPA-832-F-21-020), June 2021; read September 2026.
• City of Columbus, Department of Public Utilities, 2017 Annual Report, 2018; read September 2026.
• City of Columbus, Lower Olentangy Tunnel (LOT), Sewer Capital Improvement Projects, undated; read September 2026.
• WOSU Public Media, Three-mile Columbus sewer tunnel project reaches destination with a bang, June 4, 2025; read September 2026.
• City of Columbus, Blueprint Columbus, Blueprint Columbus home page, undated; read September 2026.
• City of Columbus, Columbus City Codes, Title 11, Chapter 1145, sections 1145.80 through 1145.89, Stormwater, as amended through 2024; read September 2026.
• City of Columbus, Blueprint Columbus, Lateral Lining, The Four Pillars, undated; read September 2026.
• City of Columbus, Blueprint Columbus, Blueprint Columbus FAQ and Resources, undated; read September 2026.
• State of Ohio, Board of Building Standards, Ohio Administrative Code rule 4101:8-25-01, Plumbing systems (Residential Code of Ohio), effective July 1, 2019; read September 2026.
• UpCodes, Chapter 11 Storm Drainage, Ohio Plumbing Code 2024, undated; read September 2026.
• State of Ohio, Board of Building Standards, Ohio Administrative Code rule 4101:3-7-01, Sanitary drainage, effective October 15, 2025; read September 2026.
• UpCodes, Chapter 7 Sanitary Drainage, Ohio Plumbing Code 2024, undated; read September 2026.
• City of Columbus, Columbus Water and Power, Project Dry Basement, undated; read September 2026.

Common questions