Water Pressure Myths Plumbing the Truth

 Few things annoy an apartment homeowner more than persistent low water pressure,  be it at the shower, the kitchen sink or the toilet. So common the problem, one  wonders what New Yorker hasn’t suffered from it and what property manager hasn’t struggled to solve it. Recently, an exasperated homeowner asked me, “Is it true I have poor water pressure because my building is old and I live on a  higher floor?”  

 Truth be told, it is a myth that water pressure is determined by the age of a  building. But, it is true that water pressure is lower at fixtures in higher  floor apartments than in lower floor apartments in buildings where the roof  tank provides the source of water. However, lower water pressure in the higher  floor apartment does not necessarily mean “poor water pressure.”  

 Separating Fact from Fiction

 To appreciate this answer, it helps to know where water pressure comes from.  Water enters the building from the New York City main at the street main  pressure which varies from as little as 30 pounds per square inch (PSI) to as  much as 90 PSI, depending upon the location of the building and the time of  day. The building’s house pump then pumps the water to the roof tank which becomes the source of  water for most of the apartments. The street main pressure can be sufficient to  feed water up to apartments as high as the sixth floor. Apartments not fed  water by the street main pressure, are sourced by the roof tank.  

 When the roof tank is used as the source of water, water pressure is created by  the force of gravity and is measured in pounds per square inch (PSI). It is calculated by using the vertical distance of the water column between the  water level at the roof tank and the plumbing fixture, and multiplying it by  .434.  

 In other words, for every one foot in distance below the roof tank water level,  the water pressure increases by .434 PSI. As an example, for a building with a  roof tank water level of two hundred (200) feet above the ground, the water  pressure at the fixtures in a ground floor apartment will be approximately 86.8  PSI (200 x 434 PSI). However, in the penthouse apartment in the same building, the water pressure  will be much lower. Assuming the penthouse apartment is located forty (40) feet  below the roof tank water level, the water pressure at the fixtures will be  approximately 17.37 PSI (40 x .434 PSI).  

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11 Comments

  • Tanks secure during earthquakes?
  • Hi Bill, I live in NYC on the 12th floor of a 13 floor apartment. My building's water does not come for a tank on the roof. I was told by my building's super today that my shower water pressure was 19 psi and that that is "plenty" and "more than adequate." Is this true? Because the pressure seems abysmal to me. Ian
  • Hello Bill - I'm a building super myself...so wanted to take the opportunity maybe to help solve your issue. One of the first and easiest things to check when you have low shower pressure is the shower head itself. If you remove the head from the pipe, and look inside where the water enters the head, you should find a screen which catches and filters sediment from the water before it enters the shower head. Remove that carefully, clean it and put it back. That alone will usually solve a waterflow problem. I don't know how your super knows you have 19 psi to your showerhead...but in my experience as a super, that number is definitely on the low side. In my booster pump buildings, I adjusted my zonal prv's to supply pressure from the upper 20's for the higher apartments to the mid 40's for the lower apartments. Good luck. Pete
  • city water pressure coming into my building from the street level is 55psi, through 6" pipes. My apartment is on the ground floor. The pipes to the bathrooms and kitchen are 0.5". What is the water pressure at the fixtures?
  • I have the low flow low pressure problem on the top floor of a 20 story pre war building. the new piper step down in size as they reach the kitchen. I was told this is code required. Is that accurate?
  • I live on the 6th. flr. in an apt. house. Water pressure that comes thru wiggles a lot. Super saying everything is fine. I should chance my faucets and aerators.
  • Riser pipe in bathroom, getting hot, but, no pressure release of steam. This is also happening in my studio area heat turns off in a minute. I get heat sometimes, again o pressure to distribute around room.
  • I have a question I'm hoping someone will know the answer to. I have been in a 7-story prewar bldg (built in 1930) for 17+ years, on the second floor. Bathroom was retiled this spring, and water was shut off during the work. None of the faucets or showerhead were replaced. I always had great water pressure; when the water was turned back on, it was not at same level I'd had the previous 17 years. I asked the super to set it back to previous level; he said a couple of things: One, that my pressure had been twice as much as anyone else's, and two, that to fix it would require replacing the showerhead and that would necessitate breaking the wall (i.e., messing up the new work that had been done, which I know is not accurate). To get to my question: How is the water pressure controlled? Is there a setting at the site of the shut-off valve? Where would that be? Thank you
  • This may not apply to older buildings in NYC, but I figured I should point it out just in case. One consideration that was missed here is the pressure requirements of various equipment. You need to check the flow AND pressure requirements for any piece of equipment. The manufacturer provides this information in their cut sheets.
  • Greg, Several possibilities come to mind. They could have reset he pressure during the work for whatever reason. Another possibility is that there may have been more plumbing work going on in the building besides just tile work. Either that, or while they were performing the tile work they inadvertently damaged a waterline somewhere behind the wall. Even a small leak could cause water pressure issues. I don't know how your shower was built...but a shower head replacement shouldn't require the wall to be opened. You should be able to swap the shower head from the shower itself. That being said, I have seen a lot of funky installations and maybe this is one of them. As far as regulating the water pressure in the building is concerned, if the engineers decided that the pressure was too high at a given floor, then they probably had the contractor install a pressure regulator upstream of your apartment. It's most likely in a locked closet that the building management supervises. They won't want people messing with that.
  • I am a building super on the UWS of Manhattan and am having a pressure issue on one of my lines. The bathrooms in my 'A' line, from the PH down to the 7th floor (21 story building, no 13th floor) have pulsating water. When the cold water is running, there is a good strong stream for a while, then after a few minutes, the water starts to pulsate. It'll stop, then start up again a couple of min later. I bled out the cold water return, there was no air in the lines, I also checked the water shut-off valves under the sink to make sure they were fully open. City pressure coming into the building is at 90PSI, and we have a PRV set to 65PSI. Any suggestions as to the cause of the pulsating water? Thank you