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).