A few days ago, I noticed a [serious issue][1] in my home: when there was an interruption of water supply from the city, the water in my circuits was depleted very fast (running backward, passing back through the water meter), and then strong air pressure kept the water meter running backward.

I want to solve this problem. My plan is to install a simple one-way valve right after the water meter.

After the water meter, the first thing I have is a device that ensures the pressure in my house stays under 2.5 bars.

This pressure-regulated device was installed by a plumber about a year ago. I wonder if this device contributed to the problem of strong air pressure backflowing from my system.

I plan to buy a simple one-way valve like this.

and install it right after the water meter (before the blue tap). That seems pretty easy to do.

However, I am wondering if there's any downside to doing this? Could this somehow create damage to my system? My biggest fear is pipes bursting inside my house, as they would be pretty much impossible to replace.

PS: I tried to contact plumbers, but I live in the middle of nowhere, and the last 2 plumbers who came actually broke more than they fixed.

EDIT : This question has been marked as duplicate. The website suggests I delete it, but when I do so, it then advises against deleting it. So please just ignore that question.

  • 1
    No, because that question was about understanding the problem. This question is about a specific modification of the system.
    – DevShark
    Nov 5, 2022 at 9:43
  • 2
    Does your water purveyor (utility) provide any specifications or documentations WRT backflow prevention? Nov 5, 2022 at 14:05
  • 4
    My water system has a "back flow preventer" to keep water from my pipes from flowing into the public mains. The device (which was installed by a licensed plumber) is mandatory. Is that what you had in mind?
    – Duston
    Nov 5, 2022 at 14:05
  • 2
    Have you called and reported this incident to your water company? I have to think they would be very interested in their system sucking the water from your home. It could be very damaging to the water heater as well as some other fixtures.
    – RMDman
    Nov 5, 2022 at 16:45
  • 1
    @DevShark Air won't weaken the pipes. The outside of the pipes are surrounded by air all the time. Hammer arrestors actually make use of pockets of air to work.
    – gnicko
    Nov 6, 2022 at 13:39

4 Answers 4


You might start having problems with water hammer after installing a valve. If a valve* is turned off suddenly, it can cause a spike in pressure in the pipe behind it. Without a non-return valve, that pressure can dissipate out through your incoming supply.

Which means that you might need to install an expansion vessel after you have installed the valve.

*and that includes electric ones on washing machines and the like.

  • 1
    @DevShark Related problem is that any water heater may be dissipating pressure from heated water by allowing the cold water side to expand back through the incoming supply. If blocked, this could raise water pressure. To prevent this, it is standard to install an expansion tank on the cold water supply to any water heater.
    – Armand
    Nov 5, 2022 at 18:37
  • @Armand thanks for your comment, that is a concern indeed. Just before the water heater, I have a pressure relief valve (see diy.stackexchange.com/questions/259793/…). Do you still feel an expansion tank is necessary?
    – DevShark
    Nov 6, 2022 at 13:40

and then strong air pressure kept the water meter running

That wasn't air pressure. Where would the air even be coming from, unless you have a constant leak??? Or left a faucet wide open after discovering it was not flowing (which would be dumb).

More likely the air pressure was steam pressure from a tanked water heater having a meltdown, or simply gravity if the water in your system is above the water meter. Remember 30' (9m) of water height = 15 PSI = 1 bar = 100kPA of pressure.

I plan to buy a simple one-way valve... That seems pretty easy to do.

However, I am wondering if there's any downside to doing this? Could this somehow create damage to my system?

YES! What if your water system in your house becomes over-pressurized? I.E. pressure above intended? What happens?

Well, without a check valve it just pushes water out to the water mains, it's an annoyance but not a danger.

But with a check valve, nothing stops the water pressure in your house from going to infinity. Well obviously something will BREAK then, and we hope it's a pipe and not a violent BLEVE from your water heater.

So anytime you install a check valve, you must also install a pressure relief valve to vent any overpressure. I.E. the same thing that was happening through your water meter, only now it's dumping onto your property somewhere. It's perfectly allowed for this relief valve to dump into a sump or drain.

  • OP stated in a comment on linked question he already had a check valve on the tank. He did not see/remember it at first.
    – crip659
    Nov 5, 2022 at 23:04
  • Thanks Harper for your response. Indeed, I have actually a device just before the water tank, I believe it is a pressure relief valve (see diy.stackexchange.com/questions/259793/…).
    – DevShark
    Nov 6, 2022 at 13:38
  • 1
    @DevShark often the device before the water tank is a check valve, and then the water tank has a pressure relief valve built into the tank as a safety feature. You'll need such a thing on the cold side too if you do that. Nov 6, 2022 at 20:59

The standard think is to install a check valve. I am sure it is code to have one installed but given you didn't even have a prv before I am not surprised you don't have one.

Mine looks like this:

check valve

  • Commonly known in the US as a backflow preventer and typically installed just downstream of the main water cutoff.
    – Armand
    Nov 5, 2022 at 18:53
  • 1
    What (in your mind) is the difference between a "check valve" and a "one way valve"? Without that information, this answer reads somewhat unhelpfully: "Q: I want to install a device that prevents water from going backwards. What should I know? A: Have you thought about installing a device that prevents water from going backwards?"
    – R.M.
    Nov 6, 2022 at 16:58
  • 1
    Backflow preventers are generally double check valves to ensure that there is no contamination. Single check valves where you are preventing backflow of potable house water into potable city water carries less risk and doesn't require as strict of a device. My area requires yearly independent testing of backflow preventers used between an irrigation system and the city water hookup. No yearly testing of check valves is required. Nov 6, 2022 at 17:57

In the US, pressure relief valves that I have seen (like those on water heaters) are rarely-used safety devices - if they trigger, one would inspect to figure out what is wrong. The pressure ups and downs from normal working of a water heater on the other hand need a more nuanced regulation, which is where expansion tanks come in.

From thespruce.com:

In a closed plumbing system, a standard tank water heater can stress your plumbing pipes and fixtures through the normal thermal expansion that happens when water is heated. This can be a problem in any closed system where water is heated. Both water heaters and boilers for home heating systems can be prone to this kind of damage unless measures are taken to prevent it. With a plumbing system, a water heater expansion tank can help minimize the risk of pressure damage to the plumbing system. (This is normally not a problem on modern on-demand, tankless water heaters—only traditional tank-style heaters are subject to this problem.

It should be noted that all hot water boilers and hot water heaters have temperature and pressure relief valves. There are required by code and by law to prevent injury during abnormal pressure and temperature changes. They are automatic and will relieve water at the appliance, but an expansion tank is essential for the systems to operate within the design parameters.

...many homes have a closed water supply system that is equipped with a one-way valve such as a backflow valve, check valve, or pressure-reducing valve (PRV). In a closed system, this extra water pressure from thermal expansion is most likely to cause damage because the extra water pressure cannot push back into the city water supply and therefore has nowhere to go.

From an article on how to install an expansion tank for a water heater:

Inside an expansion tank is a flexible rubber diaphragm that divides the tank into two sections—one of which accepts expansion water as it heats, the other which provides an air chamber that becomes slightly pressurized as the diaphragm expands into it.

diagram of system showing expansion tank

Not the answer you're looking for? Browse other questions tagged or ask your own question.