6.4 System Testing, Disinfection & Commissioning
Key Takeaways
FPC 312.5 requires a water-supply water test at not less than working pressure for at least 15 minutes, using potable-source water; it does not set a universal 100-psi hydrostatic minimum.
Air testing is prohibited for plastic piping. The 312.5 nonplastic water-supply air alternative is at least 50 psi for 15 minutes, distinct from the nonplastic DWV air test.
FPC 312.2 uses a minimum 5-foot sectional water head, the stated overlap, an uppermost-10-foot exception and a hold of at least 15 minutes.
Test-gauge increments are at most 0.10 psi at pressures through 10 psi, 1 psi above 10 through 100 psi, and 2 psi above 100 psi.
FPC 610.1 requires purging new potable systems and disinfection where required by the authority; follow its method hierarchy rather than combining unverified AWWA residual or sampling rules with the code procedure.
System Testing, Disinfection & Commissioning
Integrity testing and sanitary preparation answer different questions. A tight pipe can still contain contamination; a disinfected pipe can still leak. Under FPC 312.1, the permit holder arranges applicable tests, gives reasonable advance notice, supplies the test equipment and determines that the installation can withstand the prescribed pressure. Follow the required inspection sequence before concealment or release.
For new potable systems, 610.1 requires purging deleterious matter and, where required by the authority having jurisdiction, disinfection before use. Do not turn that conditional requirement into an assertion that every type of plumbing system receives the same chlorination process.
1. Water-Supply System Test — 312.5
On completion of the system or a portion, prove it tight under water pressure not less than its working pressure, maintained for at least 15 minutes. The test water must come from a potable source. The code does not impose a universal 100-psi hydrostatic floor. Applicable approved project requirements can require more, but never exceed component ratings or leave unsuitable equipment exposed to a test.
Prepare the rated test boundary, restrain closures, isolate equipment as required by its instructions, fill with potable water and remove trapped air. Use suitable calibrated instrumentation and the approved safe test procedure. Keep people clear of closures and potential failures; a hydrostatic test is not harmless merely because it stores less energy than compressed gas. Record the tested portion, medium, pressure, duration and observed tightness. A pressure change needs investigation rather than a passing record based only on the starting reading.
Provided project example: a plastic distribution section has 72-psi working pressure, an approved 80-psi hydrostatic test, and all exposed components are rated for that test. Hold the specified 80 psi for at least 15 minutes. An arbitrary 100-psi target is not the rule in 312.5. An air test is not a substitute for this plastic system.
Gauge Resolution — 312.1.1
| Required test pressure | Maximum gauge increment |
|---|---|
| 10 psi or less | 0.10 psi |
| Greater than 10 psi through 100 psi | 1 psi |
| Greater than 100 psi | 2 psi |
At 80 psi, a gauge marked every 2 psi does not meet the 1-psi increment limit. Exactly 100 psi stays in that same band; a test above 100 psi enters the 2-psi band. Resolution alone does not prove calibration, accuracy or a suitable operating range.
Nonplastic Air Alternative
Section 312.5 permits a nonplastic water-supply system to be tested with air at not less than 50 psi for at least 15 minutes. Sections 312.1 and 312.5 qualify that allowance by material; 312.3 expressly prohibits air-testing plastic. Manufacturer permission does not erase that code prohibition.
Where a nonplastic air test is allowed, component suitability, stored-energy hazards, restraints, isolation and the approved safety procedure still govern. Do not equate “nonplastic” with permission to pressurize any attached device. The 50-psi water-supply alternative must not be confused with the separate 5-psi nonplastic DWV air test.
2. Drainage and Vent Testing — 312.2–312.4
DWV Water Test
For an entire-system water test, close all openings except the highest and fill to overflow. For a sectional test, close each opening except the highest openings of the section and provide at least a 5-foot head of water. Successive tests include at least the upper 5 feet of the preceding section, so that no pipe or joint, except the uppermost 10 feet of the system, has received less than a 5-foot head. Hold for at least 15 minutes and prove tightness at every point.
The 10-foot figure is the stated uppermost-system exception, not a replacement minimum sectional head. The official may require removal of cleanouts to determine that pressure reached every part. Select rated plugs and restraints and follow the safe test plan; do not stand in a plug's potential path.
DWV Air Test
Plastic piping cannot be air-tested. For a permitted nonplastic DWV air test, 312.3 specifies 5 psi uniform gauge pressure, or enough to balance a 10-inch mercury column, for at least 15 minutes. Temperature or gasket-seating adjustments must occur before the test period. A mid-test addition of air cannot be recorded as an uninterrupted passing hold; investigate and repeat under the approved procedure. At this pressure the gauge needs increments of 0.10 psi or less. The code lists the mercury-column alternative; it is not an instruction to improvise mercury test equipment.
Final Test
After fixtures are set and traps filled, the final DWV test is visual and sufficiently detailed to determine compliance. Where smoke is used, 312.4 calls for water-filled traps, smoke introduced until it appears at roof stack openings, then closed stack openings and a pressure equivalent to 1 inch of water column for at least 15 minutes. Follow the approved smoke equipment and site safety arrangements. Do not substitute an unsupported peppermint recipe or call smoke testing universal when the clause makes it conditional.
3. Potable-System Purging and Disinfection — 610.1
First identify who prescribes the method. Use the procedure required by the health authority or water purveyor with jurisdiction. In the absence of a prescribed method, 610.1 permits the applicable procedure in AWWA C651, AWWA C652, or the procedure set out in 610.1 itself. These are complete method choices, not interchangeable fragments. C651 concerns water mains and C652 water-storage facilities; select the applicable method and edition for the installation.
For a project selecting the FPC 610.1 procedure, use the following sequence:
| Step | FPC procedure and acceptance decision |
|---|---|
| Preliminary flush | Use clean potable water until dirty water no longer appears at outlets. |
| Chlorination and standing | Fill the system or isolated portion with at least 50 mg/L chlorine for 24 hours, or at least 200 mg/L for 3 hours. Valve off and maintain the selected standing period. |
| Final flush | Following the standing period, flush with clean potable water until chlorine is purged. |
| Contamination remains | Repeat the procedure where bacteriological examination shows remaining contamination. |
The code text does not add a universal 2.5-ft/s flushing velocity, 10/25-mg/L final residual pair, or two negative samples 24 hours apart to this FPC procedure. Such conditions need an applicable complete prescribed method; do not label them mandatory simply by adding “AWWA” to the heading. Sampling locations, collection materials, laboratory handling, acceptance results and release authority must follow the actual applicable plan.
Schedule example: the approved project chooses the FPC 50-mg/L, 24-hour route. Filling and isolation finish at 08:00 Monday. The standing period ends no earlier than 08:00 Tuesday, after which the final flush and remaining acceptance checks occur. A passing pressure test at noon Monday does not shorten that period. If bacteriological examination then finds contamination, the FPC procedure must be repeated; elapsed standing time alone is not release evidence.
Chlorine Mass Is Not a Product Dosing Recipe
For a provided 800-L isolated volume, a 50-mg/L target represents 800 × 50 = 40,000 mg = 40 g of chlorine. At 200 mg/L it represents 160 g. Those are concentration-times-volume calculations only. Actual product quantity depends on available-chlorine strength, solution density where relevant, chlorine demand, mixing, compatibility and the approved procedure. Never equate 40 g of chlorine with 40 g of any bleach product or mix incompatible treatment chemicals.
Disposal and Release
Plan collection, treatment and the authorized discharge destination before chlorination. Chlorinated test water can harm aquatic organisms; a storm inlet or retention pond is not an automatically authorized disposal point. Follow the receiving authority's discharge conditions and an approved dechlorination procedure where treatment is needed. A measured residual below an invented universal 0.1 mg/L limit does not by itself authorize discharge. Chemical treatment, dilution and the destination are separate decisions.
Provided disposal case: a project prohibits storm discharge and requires collected water to be treated and accepted by the designated wastewater receiver before release. A low residual reading does not cancel the destination restriction. Retain the test, flush, treatment, sampling and acceptance records required for the project, and release the system only after its applicable conditions have been satisfied.
A new plastic water-distribution section has 72-psi working pressure. Its approved rated test plan specifies 80 psi hydrostatic, and no other pressure requirement applies. Which record is consistent with FPC 312.5 and that plan?
50 psi air for 15 minutes because the pressure is below the working pressure.
80 psi using potable-source water for at least 15 minutes, with the section proved tight.
100 psi water for 5 minutes because 100 psi is the universal code minimum.
72 psi water for 10 minutes because the working pressure has been reached.
A contractor proposes a 5-psi air test on PVC DWV rough-in, using a calibrated 0.10-psi-increment gauge. What is the correct review under FPC 312.3?
Accept it because the gauge meets the resolution requirement.
Accept it if the hold is extended from 15 to 30 minutes.
Reject the air method for plastic and use the applicable approved water-test arrangement.
Accept it if the pipe manufacturer gives written permission.
No authority-specific method is prescribed. A project selects the FPC 610.1 procedure with at least 50 mg/L chlorine, finishes filling and isolation at 08:00 Monday, and has a pressure-test approval at noon. What is the earliest correct next-stage schedule?
Complete the standing period at 08:00 Tuesday, then perform the required final flush and remaining acceptance checks.
Release at noon Monday because the pressure test establishes both tightness and cleanliness.
Start the final flush at 20:00 Monday because 50 mg/L requires only 12 hours.
Release at 08:00 Tuesday without flushing because the standing period has ended.
An approved project disposal plan prohibits storm discharge and requires collection, treatment and acceptance by a designated wastewater receiver. After disinfection, a technician measures a low chlorine residual. Which action is justified?
Discharge to the nearest storm inlet because low residual overrides the plan.
Dilute into a retention pond because pressure testing has passed.
Continue the specified collection and acceptance process; residual alone does not authorize a different destination.
Release to any sewer as soon as a neutralizer has been added.
Sections you finish are checked off in the contents.