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How to pressure test plumbing

Updated April 17, 2017

When you install new plumbing during home construction or a renovation project, local building codes may require a building inspector to conduct a pressure test. In order to avoid excess fees or a failed inspection, you may want to conduct your own pressure test in advance of the inspection. Even if an inspector will not be pressure testing your pipes, you can use a pressure test to verify the quality of the installation and to identify and address any problems before they become more serious.

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  1. Prepare the system. Ideally, you should test water supply and DWV (drainage, waste and vent) pipes when the entire system is installed, but nothing is covered by drywall or otherwise inaccessible. The pipes should be dry and the main water supply turned off.

  2. Block DWV pipes. To pressure test plumbing, you need to start with an airtight system. Block the vent and drain pipes at T-fittings close to the main stack, and plug all openings such as drains and fixture stub-outs. You can do this by using solvent-glued plastic caps or inflatable test balloons.

  3. Connect air pump and pressure gauge. Following the manufacturer's instructions, connect the air pump and pressure gauge to your DWV line at a convenient access point, such as a cleanout fitting.

  4. Pressurise the system. Run the air pump until the pressure gauge registers five pounds per square inch (PSI).

  5. Monitor pressure. Check the pressure gauge periodically for at least 15 minutes. If the pressure remains unchanged at five PSI, your DWV lines are airtight and have passed the pressure test. If the pressure falls, you probably have a leak somewhere.

  6. Check for leaks. Even if your pressure remains constant, you may want to trace the path of your DWV pipes and check for any signs of a slow leak, such as a soft hiss of escaping air. If the pressure falls during your test or you suspect a leak for any other reason, you can also check fittings by applying a little soapy water and watching for bubbles created by moving air.

  7. Fix leaks. Once you have identified the source of any leak, you can address the problem by reseating or replacing loose or faulty fittings or compromised sections of pipe. You can then conduct a new pressure test to confirm that the problem is solved or discover what remains to be done.

  8. Test water supply lines. You can generally pressure test water supply lines by simply turning on the water and checking the entire length of the system to spot any leaks, which the water pressure should reveal. If you prefer an air pressure test, however, you can follow the same steps as with the DWV pipes.

  9. Tip

    You can purchase necessary equipment and supplies at hardware or plumbing supply stores, but it may be more cost-effective to get everything from a tool rental business. Check your local building codes or call a licensed inspector to verify whether a pressure test is necessary and learn any specific requirements, such as the testing pressure and length of time.


    When conducting an air pressure test, wear safety goggles and other protective equipment, and be extremely careful, especially when checking joints and seals. High pressure could cause loose fittings to fly off at high speed or create other potential hazards.

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Things You'll Need

  • Pipe caps or test balloons
  • Air pump
  • Pressure gauge
  • Stopwatch or clock

About the Author

Will Capra

A copywriter and editor since 1998, Will Capra has handled projects for Fortune 50 companies, health care and higher education institutions and nonprofits, and his work has garnered numerous awards. Capra is also a prolific online writer, covering topics ranging from travel to technology for eHow. Capra holds a B.A. in English and is pursuing a master's degree in the same subject.

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