Reviewed August 16, 2026. Fats, oils, and grease (FOG) can obstruct sewer systems and contribute to wastewater overflows. The strongest national evidence supports that practical conclusion, but it does not support many widely repeated claims about FOG causing a fixed share of every U.S. sewer overflow.
What the EPA evidence actually says
The U.S. Environmental Protection Agency currently estimates that the United States experiences at least 23,000 to 75,000 sanitary sewer overflows a year, excluding backups into buildings. EPA lists several possible causes, including blockages, line breaks, excess groundwater or stormwater, power failures, design problems, and vandalism.
An EPA food-service fact sheet cites a 2004 EPA Report to Congress finding that grease from restaurants, homes, and industrial sources was the most common cause of reported blockages, at 47%. That is not the same as saying FOG causes 47% of all current U.S. sanitary sewer overflows. The date, population, and measured event must stay attached to the statistic.
EPA says sanitary sewer overflows can contaminate water, damage property, and threaten public health. EPA also identifies controls that limit FOG entering sewer systems as one of several ways communities can reduce overflows.
How FOG can reach a waterway
FOG discharged to a drain can cool, accumulate with other materials, and reduce sewer capacity. If a blockage or another system failure leads to an overflow, untreated or partially treated sewage may reach streets, buildings, streams, rivers, lakes, estuaries, or coastal waters.
Animal fats and vegetable oils can also cause direct environmental harm when spilled. EPA notes effects such as coating plants and animals, oxygen depletion, habitat damage, odors, and fouling of shorelines or treatment facilities. Those spill effects should not be converted into an unsupported claim that every grease-interceptor incident produces the same outcome.
Where grease interceptors fit
EPA describes grease traps and interceptors as on-site devices that collect FOG before it enters a municipal wastewater system. They are one part of a broader program that may also include kitchen practices, inspections, maintenance records, local discharge limits, transporter requirements, and enforcement.
A device does not prove compliance by itself. Its type, sizing, installation, use, inspection, and service must fit the requirements that apply at the facility. Local wastewater or pretreatment authorities may use different terminology and rules.
Practical controls for a food-service operation
- Keep used cooking oil and pan grease out of sinks and floor drains.
- Scrape or dry-wipe food and grease from wares before washing where local guidance recommends it.
- Use sink screens or other allowed solids controls and empty them into the proper waste stream.
- Inspect and service grease-control equipment under the locally required plan and actual operating conditions.
- Keep the service, transport, and receiving records required by the local program.
- Report a backup or suspected release through the facility’s emergency procedure and the contacts required locally.
For equipment-specific planning, use the commercial kitchen plumbing guide. For maintenance decisions, see the service-frequency guide.
Frequently asked questions
Does FOG cause nearly half of all U.S. sewer overflows?
No current EPA source reviewed for this article supports that statement. EPA’s 47% figure concerned reported blockages in an older national report, not every current sanitary sewer overflow.
Does a grease trap capture all FOG?
Do not assume complete capture. Performance depends on the device, installation, loading, use, condition, and maintenance. Follow the equipment instructions and the controlling local program.
Are FOG rules federal?
Federal pretreatment rules provide a national framework, but municipalities and other control authorities commonly administer facility requirements, permits, limits, records, and enforcement.
Can captured grease always become biodiesel or compost?
No. Receiving and recovery options depend on the waste stream, contamination, local permissions, and the receiving facility. Confirm the actual destination with the service provider and local authority.
Official sources
- U.S. EPA: Sanitary Sewer Overflows
- U.S. EPA: Sanitary Sewer Overflow Frequent Questions
- U.S. EPA: Controlling FOG Discharges from Food Service Establishments
- U.S. EPA: Vegetable Oils and Animal Fats
Author: Grease Trap Locator Editorial Team
The Grease Trap Locator editorial team covers FOG compliance, grease trap maintenance, and commercial kitchen regulations across the US and Canada. Our guides are written for restaurant owners, facility managers, and food service operators who need practical, accurate information without the fluff.
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