Commercial Construction
Cosmos Corporation
Full plumbing build-out at 601 Pearl Dr, St Peters, MO — office and warehouse systems.
Commercial Plumbing Contractor · St. Louis Metro
St. Louis Commercial Plumbing, Built on Legacy
Ground-up new construction, underground site utilities, and complex commercial systems across the whole St. Louis metro area — backed by a full-service division for repairs and maintenance.
Licensed & Bonded Self-Performing GC Partner Scheduled Service (7am–3:30pm)
Contact Us
Tell us about your project — we respond same business day.
25+
Years Experienced
100%
Workmanship Guarantee
30+
St. Louis Metro Cities
5-Star
Customer Reviews
Any Size, Any Scope
From $500 Service Calls to $5,000,000 Builds
A leaking faucet on a Saturday night or a ground-up healthcare campus — the same Legacy crew shows up with the same standards, the same tools, and the same accountability.
Service & Repairs
Tenant Build-Outs
Industrial & Warehouse
Medium Commercial & Office
Healthcare & Medical
Underground & Site Utilities
Multi-Unit Residential
Design/Build Mega-Projects
Modern Plumbing, Built on Legacy
State-of-the-Art Techniques on Every Project
BIM/VDC preconstruction, off-site prefabrication, ProPress, trenchless CIPP lining, hydro-excavation, and IoT leak monitoring — modern tools in the hands of union-trained Local 562 craftsmen.
- BIM / VDC Coordination
- Off-Site Prefab Skids
- Trenchless CIPP Lining
- Smart Leak Monitoring
What We Do
Commercial Plumbing Services in St. Louis, MO & Surrounding Areas
Self-performing commercial plumbing for general contractors, developers, and facility owners — plus a service division that handles everything after the ribbon-cutting.
Design/Build Commercial Plumbing
Full design/build delivery for ground-up commercial construction across the St. Louis metro.
Learn moreNew Construction Plumbing
Underground rough-in, top-out, trim-out, and final inspection coordination with your GC schedule.
Learn moreUnderground & Site Utilities
Sanitary, storm, water service, and grease waste underground for commercial sites and pads.
Learn moreMedical & Process Gas Piping
Brazed med gas, lab gas, and process piping installed, certified, and tested to NFPA 99.
Learn moreBackflow Install & Testing
RPZ and DCVA assemblies installed, repaired, and annually certified for code compliance.
Learn moreHydro-Jetting & Sewer Repair
Camera inspection, hydro-jetting, and trenchless repair for commercial sewer & drain lines.
Learn moreCommercial Water Heaters
High-efficiency tank, tankless, and recirculation systems sized for industrial, medium commercial, and medical facilities.
Learn moreService Division (7am–3:30pm)
Same-day scheduled service plus residential repairs, water heaters, and drain cleaning.
Learn more
Our Priority
Commercial Construction & Site Work
Ground-up new construction, underground site utilities, design/build, med gas, and tenant build-outs for St. Louis developers and GCs.
Explore commercial work →
Service Division
Service, Repair & Residential
Same-day commercial service plus residential repairs — water heaters, drain cleaning, leak repair, and remodels across the metro.
See service options →Why GCs & Owners Choose Legacy
A St. Louis Commercial Plumbing Partner That Hits the Schedule
In commercial construction, plumbing drives the schedule. Our crews show up staffed, sequenced, and ready to keep your GC timeline on track.
Self-Performing Underground
In-house excavation, skid steers, and mini-excavators for sanitary, storm, and water service.
Design/Build & Preconstruction
Early-stage budgeting, value engineering, and constructability review with your design team.
Code & Inspection Experts
Deep knowledge of MO plumbing code, backflow, med gas certification, and municipal permitting.
Service Division That Backs the Build
When the punch list closes, our scheduled service division keeps your facility running.
Service Area
Local Plumbers Across the St. Louis Metro & 2-Hour Radius
Headquartered in O'Fallon, MO and serving homeowners, property managers, and businesses across the St. Louis metro and a 2-hour radius.
St. Charles County
- • O'Fallon
- • St. Charles
- • St. Peters
- • Wentzville
- • Lake St. Louis
- • Dardenne Prairie
- • Cottleville
- • Weldon Spring
St. Louis County
- • Chesterfield
- • Clayton
- • Ladue
- • Kirkwood
- • Webster Groves
- • Creve Coeur
- • Ballwin
- • Maryland Heights
St. Louis City
- • Central West End
- • Lafayette Square
- • Soulard
- • The Hill
- • Tower Grove
- • Downtown
- • Midtown
- • South City
Featured Projects
Recent work across the St. Louis metro
From dental office rough-in to commercial site utilities, tankless installs, and service replacements — see the craftsmanship that goes into every Legacy Plumbing job.
Site Utilities
Soapify Car Wash
Sanitary, storm, and oil/water separator tie-ins for a new car wash facility.
Commercial Service
Mechanical Room Build-Out
Backflow preventer, PRV, and Bradford White water heater installation.
Commercial New Construction
Kraner Family Dental
Underground rough-in for a new ground-up dental office build.
Medical & Dental
Celebrate Dental
Plumbing and fixture installation for a new dental clinic at 7934 N Lindbergh Blvd, Hazelwood, MO.
Commercial Above-Ground
Kraner Family Dental — Rough-In
Overhead water, waste & vent piping with seismic bracing.
Service Division
Twin Tankless Water Heaters
Cascaded Rheem tankless units with manifolded copper distribution.
Service Calls
Residential & Service
Fully-stocked service vans across the St. Louis metro and surrounding region.
Trusted Industry Partnerships
Union-trained. Industry-backed.
Proud signatory and member — bringing certified craftsmanship and industry standards to every Legacy Plumbing project.
FAQSee all commercial plumbing FAQs
Frequently Asked Questions
Answers about scheduling, service area, pricing, and qualifications across the St. Louis metro.
Schedule Your Free Estimate
Tell us what's going on — we respond same business day.
Office Hours
Monday – Friday · 7:00 AM – 3:30 PM
811 N Main St, O'Fallon, MO 63366
Need a Plumber in St. Louis or the Surrounding Area?
Same-day estimates, transparent pricing, and 25+ years of trusted craftsmanship across the St. Louis metro and a 2-hour radius.