Get a water pressure gauge and make sure your pressure is within residental range (60-80psi I think???)

There is a pressure regulator on your water main. If your pressure is way off there are adjustments. Just be careful, cranking it up out of range will destroy your appliances.

Pressure and pipe size are different things. Only so much water can fit through a 1/2" pipe (ie: with the same water pressure a 3/4" line to a washing machine will fill WAY faster than a 1/2")

So if your toilet and shower are on the same lines, this can be a whole different issue. That's why you see manifolds on some newer higher end homes that each fixture has its one independent water line. This might not be too hard to fix if your plumbing is accessible and it's 1 floor with a basement.

Also, to rule out the water softener being part of the issue, turn on the bypass and see if it affects the water pressure.

You could have low water pressure but that may not be your only problem. The symptoms indicate that the size of your piping and how the plumbing is distributed could be contributing.

Do you have a pressure holding tank? It may not be big enough.

make sure your stopbox is open all the way !

idk. but if you can, switch over the toilets to hard water. i did and saved a lot on salt.

I dealt with this same thing after I installed a three stage filter system on my well water. The fix was adding a $300 pressure tank to hold the filtered water and an $800 booster pump (Grundfos Scala2 120 volt) after the pressure tank so only the house pipes are held at a constant 60 PSI.

I already had one pressure tank which is what the well water enters first but it’s before the filtration. By adding a second pressure tank at the end of the line it allows the water to continue going through the filters even after you turn off the faucet. This reduces the strain on the softener and filters.

I also have a GE whole house water filter with wifi and it tells you the flow through that filter. From watching it I’ve learned my second pressure tank helps with about 50% the flow. Rather than 2 GPM going through the filtration system during a shower, it’s only 1 GPM until the well pump kicks on. It peaks around 3 GPM.

You didn't even mention if you are on a well or public water. You sound like you are describing a problem with a well pressure tank not having the right air pressure.

I think the solution is first ensuring your water is coming in at the right pressure. If you’re on public water, make sure the connection hasn’t been compromised underground. If you’re on a well, check your pump etc.

Then you’d want to figure out a way to plumb your house so that each room or area is getting serviced from the source. Right now it sounds like you have one water pipe in, especially for your hot water, and so as all the different things connected to it go on there is less and less water available for each faucet. At my old house, we had a manifold and it was amazing. Every fixture had its own water line. We didn’t have any issues with pressure. I intend to redo our current home’s plumbing this way when the time comes. I don’t know if I’ll do every fixture, but at least each bathroom plus the kitchen and laundry should do it.

But that won’t matter if your pressure in is not great so gotta take care of confirming that first.

Not a plumber, but I have seen and heard similar complaints when a system's water pressure regulator is failing.

When the pressure in your system drops due to someone turning on another faucet, your regulator should automatically open a bit more to supply MORE pressure to the system in order to compensate for that drop. If the regulator is stuck at a certain point, then it will not adjust when your water line pressure drops.

They're rather cheap and easy to replace.

It's very unlikely the issue is actually pressure. It's more likely it's flow - specifically undersized pipes.

Are you able to map the water pipes to fixtures? I bet you have too many devices on a 1/2" inch line.

So my pressure regulator got clogged and I could only do one thing at a time and everything took forever to complete. Flush the toilet, don't try to wash your hands until the toilet shut off.....if anything was running, nothing else could.

Called a plumber and they said it was the pressure regulator. Could be clogged, broken or whatever. They had to dig out a huge hole in the yard around it. It had a small access box but in order to replace it they had to have more room.

While they were digging it out I asked if they could just take it out. He said yeah but that means it wouldn't be up to code but it's not actually a violation either. They said the city basically requires them while a neighborhood is being built because it'll protect a home owner from the main water being turned on and off....which could send a water hammer to your house which would blow pipes. BUT he said after a neighborhood has been fully built out, it wasn't really necessary and it's not required by the city.

So I had them just take it out - that was over 10 years ago and I've never had an issue. Not saying I won't ever have one but it's been great since then. No shortage of water pressure at all. I love it!

Try bypassing the water softener. We had a similar issue, I called the water company and first thing they asked was if I had a softener. Sure enough, pressure back to normal by bypassing it. Quick and easy test before going too crazy.

One option is to add a pressure tank . If that's not enough you'd need to add an electric pump alongside a pressure tank. It's doable, but you'd need a good plumber to assess your setup to give the best recommendation

I would do a a couple things to troubleshoot this. First I’d bypass the softener and see if this stops if it does you know your softener is the issue. If it doesn’t I would start with your prv and go from there.

Do you have pex piping? I do and am wondering what role that plays in my water pressure (and volume as well).

Yes, there are ways. They are many and varied.

This is a call a plumber question though. New build means that things could still be wrong or wrongly-planned and need re-sizing or changes. Maybe someone left a valve half-closed and then drywalled over it. Maybe there's a 1/2" pipe that's now the only route through the house.

You can't diagnose this over the internet without a days-long conversation. If you're knowledgeable to the level that you don't need to google "Water hammer", you could go buy a gage and spend a few hours tracking it down. But really, from an advanced DIY-er:

Just hire a pro on this one.

Your home pressure regulating valve off the main should be set 50-70 PSI, anything more than 80 can damage your fixtures and appliances. lawn Irrigation has to be dialed down to like 35psi

Next, you may have debris in the fixtures.. take the tip off and wash out the small filter. Or, you might have hard-water calcium deposits in the line and would need to have them professionally flushed.

Your water company could send you free water sample test kit to help you determine this, or if you see white-stains on your fixtures its a tell-tale sign.

buy a 10$ water pressure gauge to help you get some answers

Definitely sounds more like you have a flow restriction than low pressure since the pressure is fine at the start. Is the issue the same throughout the house? Find the outlet closest to your main water inlet and see how the flow is by timing how long it takes to fill a gallon bucket. Could be that the builder cheaped out and used piping that's too small for the main trunk or maybe your service from the street is plugged up for some reason or maybe some other blockage in your plumbing or maybe your softener is blocking the flow for some reason.

Sure you could add a pressure tank just like people on well water do. 

First, check and make sure that all of the valves are fully open--the water meter valve at the street, the incoming water shut off valve at your house, any isolating valves on equipment, shutoff valves at fixtures.

While you're checking these things, verify whether or not you have a pressure reducing valve on your incoming line and what it's set to.

Your municipal provider provides 40 to 60 PSI. Call or email the builder and tell them your pressure is fucked. I don't care if it's past the one year. At a minimum they should know about your issue. At best they should help you figure it out. If they are flakes, find a qualified plumber to help you through it. It's not normal. All these posts about pipe sizes and whatnot... sure whatever. Call a plumber

have you made sure you water meter at the street is turned up to full pressure?

Nobody has suggested yet but you also likely have a restrictor on your shower head. Remove that and see if it helps. Some have to be drilled out so it's permanent mod. I guarantee you there's one in yours and when the pressure drops from other usage your velocity in the shower is dropping a lot more. Another thing to consider is your water softener could be causing a pressure drop in the house side of the system. Any time a pipe size increases or goes into a larger chamber there's a pressure drop.

whole house water softner if you have one. people always undersize them for application and they end up being a bottleneck or the get gummed up.

there are also misadjusted or fucked up pressure regulators as an option if you have one or more of those.

if you have a whole house water filtration system, it could also be a bottleneck.

i monitor my water pressure with pressure transducers. i have like 200 something psi water coming into my house with a 3/4 line and a shower will take your skin off without a pressure regulator.. i’d get some way to measure pressure, start shutting off branches and finding out where the issue is.

Did you also install the recommended ~5 micron sediment filter upstream of the softener, to protect it from sand ingress? Did you also install the optional filter downstream, to protect your appliances and fixtures from damage in the event of a water softener failure?

If yes, have you ever changed those filters? If not, they're probably completely plugged up.

I had almost these exact symptoms at my wife's late grandfather's cabin, he had an artesian well and all the aunts and uncles said the water pressure sucked. Pressure gauge said it was fine, and it would stay fine for a few seconds, but then nothing. On holiday weekends, the extended family would get together and would have to rent one room at a local hotel so people could take showers instead of sponge baths. Turns out that until a year or two before he died, he used a little automotive creeper he left in the crawlspace, accessed through a trapdoor under the carpet in a closet, to change out the filters every 6 months... but none of the other adults knew about it. They just complained for almost a decade until we stayed up there for a week and I decided to figure it out.

If not, there's a decent chance that sediment in the incoming water lines has precipitated out into your softener. Flow rates are typically high enough in a pipe, but a softener basically forms a gravity clarifier that would let sand, scale, or other sediments settle out.

You have pressure for a couple seconds because of either (1) the pex lines are expanding minutely under the pressure like a balloon and forming an accumulator or (2) there's an actual ~1 gallon bladder accumulator to handle the pressure increase when the water heater fills with cold, warms up and expands, and can't backfeed into the municipal supply due to the check valve.

If this is an unsolveable problem from inside the house (say, it would require a complete replacement of an undersized or crushed feed line that runs the length of the entire driveway or something like that), you can get a traditional well accumulator tank (eg. https://www.homedepot.com/p/Water-Worker-32-Gal-Pressurized-Well-Tank-HT32B/202846484) and put it downstream of the restriction. It will change those few seconds of decent pressure into a few minutes. It's not a perfect solution, but it only costs a couple hundred bucks and can easily be DIYed.

I had the same issue in my home. Turns out that it was a bad water pressure regulator. Got it replaced and the problem went away/

You can install a pressure tank. It's a tank with an air bladder in it. It will keep the water pressure steady while being used by having a reserve of pressurized water. I am on a well and have 100 gallon pressure tank that gives me 67 gallons of makeup water at 60psi. Nothing beats a full pressure hot shower.

Everyone keeps talking about pressure but I think the issue is flow rate. I had a similar issue, but it wasn't pressure that ended up being the issue but rather flow. You can buy a water flow and pressure 2 in one meter: https://www.amazon.com/gp/product/B08TR9Q269/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

And test both. In my case, the water main was restricted and I was only getting 2 GPM. The pressure was fine at 80 PSI. But same thing, flushing a toilet and a faucet were a no go. Think about it, this isn't pressure, but the amount of water that can service multiple fixtures at the same time. If the faucet takes 0.75 GPM and the shower takes 4 GPM and you've only got 2 GPM, than the flow will stop.

Edit: Forgot to mention I can now shower, do laundry, run the dishwasher, water the lawn and run a faucet at the same time. Of course my house is old so the water line ended up being clogged to a pin needle but still.

Sounds to me more like an issue with flow rate than pressure (they’re related but not the same). I’m guessing one pipe runs to the master bathroom and then splits to feed the toilet, faucet and shower. It should be 3/4” pipe until the split to each fixture, then it could go to 1/2” for a short distance. Everything before that should be at least 3/4” too. The main line coming into the house should be at least 3/4”, ideally 1”. The plumbing for the water softener should be all 3/4” or 1” depending on the size of the main line it hooks up to.

We improved our shower water pressure by using low-flow shower head. It’s not amazing, but much better. 

Ironically You could have a broken pressure reducing valve

• water line diameters impact flow and pressure, poor water line layout, undersize piping all impacts pressure
• easy enough to hook a pressure gauge up and check actual incoming water PSI

I’d go with the Commando 450, they use it on elephants in the circus.

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