Sewer System Glossary: Key Terms and Definitions

The terminology used across sewer system design, inspection, maintenance, and regulation forms a technical vocabulary shared by municipal engineers, licensed plumbers, environmental regulators, and property owners navigating service decisions. This reference defines the core terms in active use across the US sewer sector, organized by functional domain. Precise language matters in this sector because misidentified system components, incorrect permit classifications, or misunderstood regulatory terms can result in failed inspections, code violations, and infrastructure damage.

Definition and scope

The US sewer sector operates under a layered framework of federal environmental standards, state plumbing codes, and local municipal authority. The sewer-directory-purpose-and-scope page describes how this authority structure shapes service delivery across the country. The terminology below applies to both sanitary sewer systems — which carry wastewater from residential, commercial, and industrial sources — and storm sewer systems, which convey surface runoff. These two systems are distinct infrastructure categories and are governed under separate regulatory frameworks in most US jurisdictions.

The US Environmental Protection Agency (EPA) regulates the discharge of pollutants from both systems under the Clean Water Act (33 U.S.C. §1251 et seq.), while the International Plumbing Code (IPC) and Uniform Plumbing Code (UPC) govern interior and connection-point construction standards at the building level. State plumbing boards and local building departments administer permitting authority for new connections, repairs, and replacement work.

Core glossary — structural and system terms:

1. Sanitary sewer — A closed pipe network designed exclusively to transport human waste and wastewater from buildings to a treatment facility. Sanitary sewers are not designed to carry stormwater.
2. Storm sewer — A drainage infrastructure system that collects and conveys surface water runoff, typically discharging directly to rivers, streams, or retention basins without treatment.
3. Combined sewer — A single pipe system that carries both sanitary wastewater and stormwater. Combined systems are legacy infrastructure found in older US cities and are regulated under EPA's Combined Sewer Overflow (CSO) Control Policy (published 1994).
4. Lateral (building sewer lateral) — The private pipe segment connecting a building's internal plumbing to the public sewer main. Ownership and maintenance responsibility for the lateral typically rests with the property owner up to the point of connection with the public main.
5. Sewer main — The primary municipal pipe running beneath streets or easements, into which individual laterals connect.
6. Manhole — An access structure installed at intervals along sewer mains to allow inspection, cleaning, and repair by maintenance crews.
7. Invert — The lowest interior surface of a pipe at any given cross-section, used as the reference elevation in sewer surveying and hydraulic calculations.
8. Inflow and Infiltration (I/I) — The entry of groundwater and surface water into sanitary sewer systems through defective pipe joints, cracks, or improper connections. The EPA identifies I/I as a primary driver of sanitary sewer overflows (SSOs).

How it works

Gravity-fed sewer systems rely on consistent pipe slope — typically a minimum of 1/4 inch per foot for 4-inch diameter pipe under the IPC — to move wastewater toward treatment facilities. Where terrain prohibits gravity flow, lift stations (also called pump stations) use electric pumps to force sewage uphill through force mains, which are pressurized pipes distinct from gravity sewer mains.

Inspection and condition assessment use standardized methods including:

1. CCTV inspection — Closed-circuit television cameras mounted on crawler units traverse pipes internally, documenting cracks, root intrusion, joint failures, and misalignments. NASSCO (National Association of Sewer Service Companies) maintains the Pipeline Assessment and Certification Program (PACP), the industry-standard coding system for defect classification.
2. Smoke testing — Non-toxic smoke is introduced into pipe segments to locate unauthorized connections and points of surface inflow.
3. Dye testing — Colored tracer dye is introduced at a suspected connection point to confirm flow path between a structure and the sewer system. Dye testing is commonly required as part of property transfer inspections in jurisdictions with mandatory lateral inspection ordinances.

Common scenarios

The sewer-listings directory covers licensed contractors and service providers by region. The terminology above applies directly to the following operational contexts:

• Sewer lateral replacement — Triggered by CCTV-documented failures, root intrusion, or pipe material age. Cast iron and clay tile laterals installed before 1970 are frequently replaced with PVC pipe under current code requirements.
• Sanitary sewer overflow (SSO) — An unintentional discharge of raw sewage from a municipal sanitary sewer. SSOs are reportable events under the EPA's National Pollutant Discharge Elimination System (NPDES) permit program (40 CFR Part 122).
• CSO events — In combined sewer cities, heavy rainfall causes combined flows to exceed treatment plant capacity, resulting in regulated overflow discharges. As of 2023, the EPA reported approximately 772 CSO permittees operating under long-term control plans (EPA CSO homepage).

Decision boundaries

Sanitary sewer and storm sewer systems require distinct permitting pathways. Work on public mains typically requires municipal permits and licensed contractor involvement; work on private laterals requires building permits under state plumbing code jurisdiction. The additional page at how-to-use-this-sewer-resource explains how professionals and property owners can navigate service-sector resources using this directory.

The critical classification distinction is gravity main vs. force main: repair methods, materials, and inspection requirements differ substantially between the two. Trenchless rehabilitation methods — including cured-in-place pipe (CIPP) lining and pipe bursting — apply primarily to gravity mains and have material-specific approval requirements under ASTM standards (ASTM F1216 for CIPP) and local agency specifications.

References

• US Environmental Protection Agency — Combined Sewer Overflows (CSOs)
• US EPA — National Pollutant Discharge Elimination System (NPDES), 40 CFR Part 122
• Clean Water Act, 33 U.S.C. §1251
• NASSCO — Pipeline Assessment and Certification Program (PACP)
• International Association of Plumbing and Mechanical Officials — Uniform Plumbing Code
• International Code Council — International Plumbing Code
• ASTM International — ASTM F1216 Standard Practice for Rehabilitation of Existing Pipelines by the Inversion and Curing of a Resin-Impregnated Tube