Measuring domestic water pressure is a simple diagnostic that aids in understanding the performance or underperformance of showers, faucets and toilets. Simple problems, such as running toilets, banging pipes and drips from the relief valve of a water heater, can quickly be diagnosed and a repair list developed to solve those elusive problems. Start by purchasing a potable water pressure gauge with a hose bibb connection. A hose bibb connection is the female connection, which is similar to the female end of a garden hose or laundry supply hose. These gauges are inexpensive and found at most hardware or home supply stores.
Locate a hose bibb or connection in or around the perimeter of the house. This connection (also known by plumbers as boiler drains) could be the laundry tub faucet, the outdoor spigot/faucet or even the bottom of the water heater. Do not use any connections on a boiler, as the boiler is an isolated system and gives a false pressure reading for the domestic water loop.
Thread the gauge onto the male faucet or spigot, ensuring a watertight connection.
Turn off all other faucets and running water fixtures in the home if you have not done so previously.
Turn the valve on full, and note the pressure.
Turn the faucet off, and relieve the pressure on the gauge by slowly removing it from the faucet.
Repeat the procedure to ensure accurate measurements. Most plumbing codes agree that 80 psi is the maximum recommended water pressure for residential usage. Most manufacturers build their fixtures and warranty their fixtures for this rating. Most fixtures operate poorly under 35 psi.
If the water pressure exceeds 80 psi, a pressure-reducing valve should be sized and installed at the main shut-off inside the house. Night-time pressures exceed the daytime pressures by 15 psi or more due to reduced usage on the water mains.