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Plumbingaka: main valveaka: service valveaka: water main valve

Main Shutoff Valve

In Plain English

The master valve that shuts off all water to the entire building — the first thing to turn in a plumbing emergency.

Definition

The valve that controls the flow of water to the entire building, located at the point where the water service enters the structure. Turning off the main shutoff valve stops water to all fixtures and equipment, essential for emergency leak control and major plumbing repairs. It must be readily accessible and clearly identified.

Why It Matters in Bidding

On bids, the main shutoff valve marks the responsibility boundary between the utility service and the building's interior plumbing, which affects how the estimator splits scope, permits, and tap fees. Specifications often dictate the valve type, accessibility, and labeling, and overlooking required backflow assemblies, meter pits, or isolation valves at this point can create costly omissions and inspection failures.

Example

Estimating a tenant fit-out, the plumber confirms the building's main shutoff is in the basement mechanical room, so he prices only branch isolation valves for the suite and excludes any work on the building service entrance.

Related Terms

ValveDomestic WaterBackflow PreventerPressure Regulator

Frequently Asked Questions

It typically sits at the service entrance, marking the line between site/utility work and interior plumbing. On new construction the site or utility contractor may bring service to the valve, while the plumbing sub takes it from there. Confirm this boundary in the scope sheet so tap fees, meters, and backflow devices are not missed.
Depending on the project, include the water meter or meter pit, backflow prevention assembly, pressure-reducing valve, isolation valves, and required signage or labeling. Local jurisdictions and the spec often dictate specific assemblies, so reviewing utility requirements and addenda prevents undersizing the line item or omitting a code-mandated device.
Yes. If the valve is buried, hard to reach, or serves occupied areas, the estimator must price phased shutdowns, temporary water, and after-hours work to maintain service. Accessibility issues drive labor and coordination cost on occupied-building renovations and should be captured during the site walk, not assumed.

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