Once drywall, a cabinet panel or backfill covers new water treatment plumbing, a leak becomes expensive to find and repair. A pressure test done before closing-up gives you a documented check on the lines while they are still open. The steps below describe what the process should look like and what you should watch for as the homeowner.
Confirm the layout before any test
Compare the installed layout with the drawing or written plan from the installer. Check the location of each shutoff, bypass point, drain connection and test port. Make sure every fitting type matches what the plan calls for. Changes made on site are normal, but they should be marked on the plan, so the test covers the lines as they were actually built.
Cap, fill and isolate the section
The installer should cap the open ends, isolate the section being tested and fill it with water in the manner their written procedure describes. Ask which parts of the system are included in the test. Equipment such as tanks and valves may need to be bypassed or removed from the test section, and that decision should be written down.
Hold the pressure for the stated time
Use the test pressure and hold time that the installer names in the written procedure. Watch the gauge at the start and at the end of the hold. A gauge that drops during the hold points to a leak somewhere in the section, and the installer should locate it before the walls are closed. Ask what the installer will do if the gauge drops, because the answer tells you how the test will be handled if a problem appears.
Inspect every joint while the pressure holds
Look at every joint, union, compression fitting and valve connection in the section during the hold. Look for moisture, weeping, bead of water or a fitting that has shifted. Check the lines where they pass through studs, floor plates or the cabinet opening, because those are common points for stress and rubbing. Ask the installer to point out the test points on the drawing so you know what was inspected.
Record the result and close the walls
Ask for the test result in writing. A useful record lists the test pressure, the hold time, the start and end readings, the name of the person who ran the test and a note that every joint was inspected. Photograph the open lines before anything covers them. Only after the result is recorded should the walls, panels or backfill be closed. Keep the record with your installation paperwork, since it will matter if a leak appears later and you need to show where the lines were tested.