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I have city water at around 80PSI static pressure when measured at one faucet. There is some variation during the day but everything works well and I do not have a pressure regulator.

Because of unrelated trenching operation, I was thinking to update the 50+ years old water line from the meter to the house. The inspector (while checking some unrelated project) told me he sees "a lot of those lines leaking in this neighborhood". Right now, it would be very cheap to replace because the driveway is already apart.

My area requires fire sprinklers for new construction and for renovation over a certain size. I called a sprinkler company and they said to put in the biggest line I can, 1-1/2in or even 2in, so in the future I will not have to tear up the driveway again in case I want to add fire sprinklers.

Not one but two plumbing companies, one of which I already worked with in the past and has a very good reputation in town, insist that if I upsize the line I will have to install a water pressure regulator.

I cannot understand the physics of that requirement. Why is that necessary? Why is it not necessary with the 1in line I have right now?

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  • I would very much ask the companies making these recommendations why they're making them. If they have an explanation that sounds plausible, you may want to run it by the folks here to confirm that it makes sense. If, on the other hand, they hem and haw, and it sounds like they're making up something on the spot, that's a pretty good sign that they're just trying to profit.
    – FreeMan
    Aug 24, 2022 at 11:20
  • How long is your water supply line? If you're hitting 80PSI static, you should be able to get by with a 1" line provided it isn't mega-long...and even then, 1.25" should be an option (and easier to implement in common materials). Also, who do you have for a water utility? Aug 24, 2022 at 11:41
  • The employees of these companies do not really speak the same language and every time I ask why the answer is very superficial, that is why I asked here. Aug 24, 2022 at 15:49
  • Water meter to riser for the house it's about 160ft (about 50 meters). The local city of Hayward CA is the owner of the utility, May I ask why the utility matters in whether an increase in the supply line requires a pressure regulator? I recently upgraded the water meter to a bigger size because I plan to build a new bathroom Aug 24, 2022 at 15:55
  • Yeah, that's just hogwash. No-flow (static) pressure is exactly the same in a 1/16" line or a 6" line. Line size only affects how much the pressure drops from the static value under flow.
    – Ecnerwal
    Aug 24, 2022 at 16:29

1 Answer 1

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The size of the line has no bearing on the pressure except under flow. You will get the same pressure from a 1/2" line or a 2" line when the flow is off.

When you are drawing water, however, the pressure drop through the line will be greater for a smaller line.

The only time you need a pressure regulator is when the static (i.e. no flow) pressure of the municipal supply is too great. 80 psi is on the high side but not excessive.

The only explanation I can think of is that your new line will require a new tap into the main and currently there is a pressure regulator on your tap. Since that regulator is sized for the current line you will need a new larger one for your new larger line.

Unless that's the case, and the company should be able to explain it to your satisfaction, it sounds to me like the plumbing companies are just wanting to sell more expensive stuff.

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    If there were a pressure regulator near the tap on the main it would almost certainly be upstream of the customer meter - and would belong to the city and be theirs to replace. But otherwise this answer is spot on: the plumbers aren't explaining themselves well (or are simply misinformed) when they say the increased line size is their reason for recommending a regulator.
    – Greg Hill
    Aug 24, 2022 at 15:53
  • There is no pressure regulator on the house side. I can just assume the plumbers are not familiar with the actual physics of pressure lines. Aug 24, 2022 at 16:00
  • In general I would say that plumbers are not up to speed on physics. But even if the regulator is on the utility-side of the connection, you likely will have to pay for it.
    – jwh20
    Aug 24, 2022 at 17:02
  • @jwh20 I am not sure what is that I have to pay. My water pressure is just fine without a regulator and a different line size won't change that as we have determined :) Aug 25, 2022 at 2:10
  • How do you know there is not a pressure regulator now? Can you see the line from the water main to the meter and from the meter to your house?
    – jwh20
    Aug 25, 2022 at 11:03

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