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                                                                                                                                                                                                                                         April 2017

WATER PRESSURE VS. WATER FLOW 
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By: Gary Gramling
       CREIA Certified Inspector 

Recently, a friend asked me if I would check the  water pressure at  his home. His complaint was that  there was very low flow of water at his bathroom shower. So, I stopped by with my water pressure gauge which screws onto a  hose bib at the outside of the house. The pressure tested at 75 pounds per square inch (psi). The California  Plumbing Code  requires that water pressure be not less than 15 psi and not more than 80 psi.  Most  plumbers that I’ve talked with recommend that the pressure generally be at 55 to 65 psi. Within the home inspector community, the standard is generally between 40 psi and 80 psi. So, my friend’s house had proper water pressure under any of the widely used  standards. 

The reason  that  water pressure is regulated to not exceed 80 psi is that more pressure can lead to early failure and  leaks of plumbing components such as  water fittings at appliances (water heaters, washing machines,  dishwashers). Water controls such  as angle  stops (water shutoffs at sinks  and  toilets) may also prematurely fail with high water pressure. 

Water companies are not liable  for  damages resulting from supplying water at excessive pressure.  Builders are responsible for ensuring that the pressure of the water entering the home is correct.  When it comes to resales, the issue is  negotiable between the parties. 

After checking the  water pressure,, we  went inside my friend’s house and  ran the  water at the shower.  We were looking  at functional  water flow.  Water flow is only partially related to water pressure. It is  also impacted by the size  of the water piping,  the type and  age of the piping; and, the condition of the  fixture. 

In this  instance, the  other faucets in the bathroom seemed to have good flow; and, the tub faucet had what appeared  to have good  flow. But,  when I pulled the  diverter  handle at the faucet,  the flow from the showerhead was low.  Looking at the faucet,  the faucet was still  running. This was, most likely from a calcium build up that  was  keeping the  diverter from working properly and providing a good flow to the showerhead. From my experience, this is pretty common. Sometimes the buildup can be removed  by using a proper calcium  remover.  More frequently,  the faucet and diverter need to be replaced. Depending upon  individual  skills,  this may be repaired  by DIY,  a  skilled handyman or a licensed plumber.

Sometimes though, the  diverter is working properly but the shower flow is still weak.  This may need to be studied and  repaired by a licensed plumber. The  most  likely  culprit  is a bad, in the wall,  mixing valve that controls flow to the showerhead.  Most of the  time, a qualified plumber can make this  repair easily. Usually involving  soldering the fittings is required.  Not really a DIY project..