Water Pressure Measurement Location

I always measure water pressure at an outside faucet. Recently I reported high pressure on new construction. I received an email from the buyer that said:

“The plumber came to the house and measured water pressure at the cloth washer intake and was 75 psi. When I told him that you measured over 100 psi at the outdoor faucet, he said that you cannot do it at that point because outdoor faucets must be anti-siphon valves per code (to avoid sucking dirty water from a water hose in case of a system pressure drop). He added that home inspectors keep taking pressure readings at outdoor valves and that it doesn’t work in new construction houses.”

I call BS. What say you?

BS… pressure subject to change on a constant basis… pressure too high was measured at time of inspection.


Undoubtedly the front faucet branches off from the service pipe before the PR valve. Plumber is on crack.

Static water pressure is the same at all locations, with two exceptions:

  1. Once someone turns on a faucet within the plumbing system you are no longer testing static pressure, the pressure gauge will go down. (If the house is on a private well, turning on a faucet my kick on the well pump raising the pressure)

  2. If the house has a pressure regulator some plumbers will plumb the outside faucets before the regulator giving the outside faucets greater pressure than the inside faucets.

Must be a regional thing. I’ve never seen that.

Learn something new every day. :smiley:

Thanks, Randy!

Exactly how my house in Santa Barbara is done. Nice 100 psi for hoses and sprinkler system and 65 for interior.

Sure. The plumber was saying that you can’t check the pressure at an anti-siphon valve. That’s what I called BS on.

They do it to save piping. It’s a code violation. The main shutoff valve doesn’t shut off all water and the pressure at distribution piping is > 80 PSI.

From the UPC / California Plumbing Code that is used:

Where static water pressure in the water supply piping is exceeding 80 psi (552 kPa), an approved-type pressure regulator preceded by an adequate strainer shall be installed and the static pressure reduced to 80 psi (552 kPa) or less. Pressure regulator(s) equal to or exceeding 1 1/2 inches (40mm) shall not require a strainer. Such regulator(s) shall control the pressure to water outlets in the building unless otherwise approved by the Authority Having Jurisdiction.

My front exterior hose bib and sprinkler system backflows / distribution are installed on the exterior, prior to the water line entering the building. They are within code. My rear hose bibs come off the main line after it enters the building and are covered by the pressure regulator.

Don’t expect the builder to understand and quote the plumber any more accurately than they quote what you say.

Builder probably doesn’t know a pressure regulator from an anti-siphon from a mixing valve.

Mulling all this over and having the following thoughts:

I can see no way that an anti-siphon device would give an erroneously high reading.

I can see that it would be possible for hose bibs to be under a different amount of pressure than other plumbing if the other plumbing is subject to regulation.

I can also imagine you would have slightly lower water pressure on the second floor than on the first floor, and that how much would depend on the height of the tower supplying the water.

According to the 2015 IRC, the exterior faucet is part of the water distribution system and its pressure shall not be higher than 80 psi. There is no exclusion for fixtures not “in the building” in the IRC.


The vast majority of exterior faucets are from the main line distribution after it enters the home. Mine are not. Also, the IRC is not applicable for my home. I posted the codes in use so your’s mean nothing.

I posted the IRC for other’s edification.

There aren’t any states that use the IRC for plumbing. Most are either UPC, IPC or a specific State code.

The IPC also has wording for “in the building” water distribution piping but also has an exception for outside sill cocks and outside hydrants.

34 states use the IPC
11 states use the UPC
8 states use their own or are based on either UPC or IPC
New Jersey uses NSPC.

You are wrong. SC has for a long time adopted the IRC.

Guess you are a little behind the times.

Table of Contents | ICC publicACCESS

Guess you are a few years behind…


Mandatory Building Codes adopted for current use in South Carolina and which must
be enforced by all municipalities and counties, beginning July 1, 2016, include the:
2015 South Carolina Building Code or the 2015 International Building Code with SC modifications;
2015 South Carolina Residential Code or the 2015 International Residential Code
with SC modifications;
2015 South Carolina Fire Code or the 2015 International Fire Code with SC

2015 South Carolina Plumbing Code or the 2015 International Plumbing Code.

2015 South Carolina Mechanical Code or the 2015 International Mechanical Code.
2015 South Carolina Fuel Gas Code or the 2015 International Fuel Gas Code with
SC modifications
2009 South Carolina Energy Conservation Code;
2014 National Electrical Code (NFPA 70).

I see. It’s lecture time from WA know-it-all with too much times on his hands.

Logic would dictate that I know a tad more about the codes in use in SC and NC where I live and work. For the record , I worked full-time as a licensed BUILDING OFFICIAL in SC up until a few years ago and managed the Building Dept in a small town during the Great Recession.

To clear up your confusion, the general practice in most SC jurisdictions is that the IRC governs all aspects of residential construction–building, mechanical, electrical, and plumbing. With the exception of the IECC, most jurisdictions do not enforce the IPC, NEC, IMC, etc. except for commercial construction.

Hope that helps. When you get one of these, then we can debate some more about our local codes.