Pressure Testing, Inspection, and System Commissioning

Why Pressure Testing Matters

A water supply rough-in that passes a pressure test before the walls close is a system the inspector, the contractor, and the building owner can trust. A leak discovered after drywall is hung costs far more to fix than one found during testing. More importantly, an undetected leak behind finished walls can cause structural damage, mold growth, and health hazards. Pressure testing is not a formality — it is the last quality checkpoint before a system is hidden from view.

This lesson covers hydrostatic pressure testing of a completed water supply rough-in: how to set up the test, execute it correctly, read and record results, and produce a test record that satisfies an inspection.

What Is a Hydrostatic Test?

A hydrostatic test fills the piping system with water (not air) and raises the internal pressure to a specified level above normal operating pressure. Water is used because it is nearly incompressible. If a fitting fails under hydraulic pressure, the stored energy releases slowly and the leak appears as a drip or spray. Air or gas under the same pressure stores far more energy and can cause sudden, dangerous rupture — never substitute compressed air or nitrogen for a hydrostatic test on a water supply system unless the applicable code and your instructor specifically authorize a pneumatic test and all pneumatic-test safety controls are in place.

Code Requirements

Before you touch a gauge, look up the required test pressure and hold time in the code that governs the jurisdiction where you are working. The International Plumbing Code (IPC) and the Uniform Plumbing Code (UPC) both specify minimum test pressures and durations for water supply piping. The values are not identical between the two codes, and a state or local amendment may change them further. Always verify the current adopted edition for your jurisdiction. Record the code section, the required pressure, and the required hold time on your test log before you begin — an inspector may ask you to cite them.

Pre-Test Preparation

Proper setup prevents false failures and unsafe conditions.

1. Cap all open stub-outs. Every open end of the rough-in must be sealed with an appropriate end cap or test plug rated for the test pressure. An uncapped stub-out will simply spray water when pressurized.

2. Install the test gauge at the low point. Pressure is highest at the lowest point in the system. Reading the gauge at the low point gives you the most conservative (and accurate) measurement. Use a gauge with a range of at least 1.5× the test pressure — a 0–200 psi gauge is appropriate for most domestic water supply tests.

3. Connect the fill hose and hand pump. The hand pump allows you to raise pressure slowly and in a controlled manner. Attach the fill hose to a convenient inlet and confirm all connections are tight.

4. Set all valves to the correct position. Every valve in the system being tested must be open so that the full pipe network is included. Valves downstream of the system boundary (such as at fixtures) should be closed or capped.

5. Instructor review. Do not begin pressurizing until your instructor has reviewed the setup and given approval.

PPE and Safety

• Safety glasses are required any time you are working on a pressurized or about-to-be-pressurized system. Water under pressure can spray without warning.
• Gloves protect your hands during soldering repairs and when handling wet fittings.
• Keep a bucket and dry rags nearby to manage any water released during depressurization or leak repair.
• Never exceed the test pressure called for in the code or the pressure rating of the weakest component in the system, whichever is lower.
• Depressurize the system fully before making any repairs.

Executing the Hydrostatic Test

1. Fill slowly. Open the fill valve and allow water to enter from the bottom. Fill at a slow rate to push air upward.

2. Bleed air at the high point. Air trapped in the system compresses and gives false pressure readings. Open the highest stub-out or cap slightly until a steady stream of water (no bubbles) flows, then reseal it.

3. Raise to test pressure. Use the hand pump to bring pressure up to the required level. Watch the gauge and stop pumping at the target value. Do not overshoot.

4. Record the start reading. Note the time and gauge reading on your test log.

5. Hold for the required duration. Do not add pressure during the hold period. Any pressure drop indicates a leak.

6. Record mid-point and end readings. Log the gauge reading at the midpoint of the hold and again at the end. A stable gauge reading across all three points is a passing test.

Leak Location and Repair

If pressure drops, depressurize the system fully before you do anything else. Then:

• Perform a visual inspection — look for wet spots, drips, or mineral residue at joints.
• Use the dry-hand touch method — run a dry hand along joints and fittings; moisture will transfer to your skin before it is visible from a distance.
• Document the location, joint type (soldered, press, PEX crimp, threaded, etc.), and failure mode (e.g., incomplete solder fill, loose crimp ring, cross-threaded fitting) on the defect log.
• Make the repair using the correct technique and materials for the pipe type.
• Re-test the full system from the beginning. A repair that holds at fill pressure may still fail at test pressure.
• Continue the repair-and-retest cycle until the system passes.

The Test Record

A complete, signed test log is as important as the test itself. It is your legal documentation that the system was tested. The record must include: date, project or mock-up identifier, code reference and required test pressure, required hold time, actual gauge readings at start/midpoint/end, a clear pass or fail result, and your signature. Any repaired joints must be listed on the defect log with joint type and failure mode. Submit both documents to your instructor.

Connection to Your Credentials

Pressure testing procedure and interpretation appear on the NCCER Plumbing assessments at Levels 2 and 3. Mastery of test setup and documentation is also directly assessed on the State Journeyman Plumber licensing examination. Backflow prevention assemblies tested under ASSE protocols also require documented pressure testing, making this skill foundational across all three credentials you are pursuing.