I bought a house and found out too late that it appears the entire upper floor is supplied from one small pipe. So if you flush the toilet or wash your hands while someone is in the shower, they get burnt (cold water pressure drops, only hot water is left coming).

I know nothing about plumbing, but I was wondering if I have any options to fix this. Replacing the piping seems out of the question as it would require opening walls, floors, the lot.

My main concern is the shower. If the sink flows slightly less, or the toilet needs longer to fill back up - that's fine with me. But I'd like to take a shower without warning everyone not to use the toilet.

But what, exactly, are my options?

Edit: Additional information: I'm on city water. The house is about 5 years old, so pipes aren't old. The previous owners simply put in too small pipes.

  • What diameter pipes do you have?
    – Freiheit
    Commented Sep 27, 2017 at 13:08
  • A diagram might help too, but thats bit of effort to create.
    – Freiheit
    Commented Sep 27, 2017 at 13:08
  • 1
    I don't have a diagram myself, trying to get one from the original builder. The pipe seems to be 1/2 inch, give or take a bit. Another guy who came for the heating system (floor heating) pointed out to me that the pipe seems small. I do have considerably more water pressure in the garden outlet, which is connected by a different pipe directly from the main (and is only cold water).
    – Tom
    Commented Sep 27, 2017 at 15:22

2 Answers 2


Try turning up the pressure of water in your house.

Many municipalities supply water with far greater pressure than you need, and you will have one of these 'pressure regulating valves' (PRV) in your basement, or perhaps in the meter pit.


Be careful that you don't turn it up too high though. It's there to protect things from bursting. I'm happy with 35psi, I think 75psi is a good max upper limit, but you should google your water heater, ice maker, and anything expensive that's connected to the water supply.

To measure pressure before you adjust, you can pick up a water pressure gague too. It's worth it before you go messing with this. water pressure gague In my house there's a spigot with unregulated pressure BEFORE the PRV, and there's a spigot on the hot water heater AFTER the PRV, for you to compare.

Adjusting the PRV will affect the pressure of water everywhere in your home. So if you wanted to ONLY increase it upstairs you'd need to add a second PRV to your system, install a second hot water heater, and plumb the upstairs separately.

A word of caution. Even if everything is rated to handle the higher pressure, the day you turn it up, if something has weakened over time that you don't know about that's likely to push it over the edge, so be ready to deal with a leak.

To know if there's a leak:

Leave that pressure gauge on, and get a baseline for any natural leak rate before you adjust the PRV. To do this, turn off all sinks/showers/appliances, write down the pressure, then shut off the water supply to the house. The pressure should stay the same. Wait 24 hours, and make note of any pressure drop. Repeat several times until you have a consistent expectation of how pressure normally drops over the course of 24 hours.

You could use a shorter duration of time, like 6 hours, but be consistent when you re-test so you can get a consistent reading.

Repeat this testing AFTER your adjustment. If the pressure goes down much quicker after the adjustment there's a leak somewhere. If it's not obvious where, you might be able to find it using FLIR imagery taken before and after the adjustment.

  • I cannot cite why, but this advice seems risky to me. The effort to increase pressure, monitor that pressure, and address the risks seems greater than the effort required to fix the fundamental problem and add supply lines.
    – Freiheit
    Commented Sep 27, 2017 at 13:07
  • 1
    OP said replacing pipes was out of the question. I thought I was pretty clear on the risk. If everything is properly constructed, nothing ought to be bursting shy of 120psi, but sinks in the basement are sure going to want to spray all over the place! Commented Sep 27, 2017 at 13:11
  • I think the basis of my gut reaction is that, as OP states, this is newer construction and the owner cheaped out on pipe diameter and plumbing design. That makes me wonder if they cheaped out on other connections that might not take the pressure. You're right, increasing the pressure will increase flow and you've laid out how to measure that and mitigate risk. I'm trying to learn more rather than criticize your answer, I hope I did not come off as rude or argumentative.
    – Freiheit
    Commented Sep 27, 2017 at 13:22
  • Sorry for the late reply. Is there any way to detect a possible leak if it's not visible, e.g. a change in pressure or something? I finally found such a valve and I'm thinking to increase pressure just a little bit but yes, since the previous owners cheaped out on the pipes, I'm a bit scared.
    – Tom
    Commented Oct 28, 2017 at 11:04
  • Detecting WHERE it's leaking is much trickier. But detecting THAT it's leaking, could be done by watching the pressure and shutting off the main valve, which should be right near that PRV. I'll add details to the answer. Commented Oct 28, 2017 at 13:05

It sounds like your shower valve does not have an anti-scald valve installed to protect people from this problem.

  • You could replace the shower valve with an anti-scald valve.

  • You could add an anti-scale valve in the lines going to the upstairs.

These solutions will not bring more water to the bathroom though. When someone flushes the toilet you will still get low flow to the shower. To solve that you need bigger pipes or raise the existing water pressure in the system. So...

  • You could replace the main lines feeding the upstairs with larger pipes. The small pipes in the walls feeding each fixture could be skipped. It is the main supply that is mostly restricting your flow. Especially if it is old corroded galvanized pipe. The corrosion could seriously restrict the flow.

  • You could increase the pressure if you are on a well. (This brings with it the hazard of creating leaks where there were none before) If you are on city water then you don't have this option.

  • You could do a combination of some of the above to achieve your goal.

I would recommend adding the anti-scald valve in a convenient location. Adding it to the shower may require removing a tile wall if you don't have an access panel, this would be very expensive. In that case I would add an in-line valve in the supply lines. I would also increase the size of the supply lines to increase your supply flow. After both of these, your problem should be nearly eliminated.

Good luck!

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