Turning on the shower and discovering that you have such low water pressure that you can't get the shampoo out of your hair is frustrating - especially if, like my daughters, you have rather abundant hair. The good news is that it is relatively rare, much rarer than high water pressure. The cause can be fixture specific, system specific (all the hot water lines are affected) or, in the case I had last week, affecting the whole house.
Testing for water pressure is not part of the Washington State Standards of Practice for home inspectors. Still, it isn't hard to do and can give the inspector clues on conditions inside the home.
In the photo to the side, you can see the gauge is reading about 32 PSI (pounds per square inch.) The water pressure I expect to see in normal residential housing is 40-80 PSI so this was definitely on the low side. A quick check inside allowed me to verify that nobody was using water and pulling the pressure down.
There are a half dozen considerations that must be taken into account when I see a reading like this. The age of the home is the first. If this were an older home, I may be looking at a main supply line that is corroding/failing.
Likewise, the individual line to the bib might be failing so determining the material is important - some materials degrade faster than others.
The answer I don't want to arrive at is that the municipal supply is that low. Without a booster system, which isn't horribly expensive but still an additional cost, what you see is what you'll shower with.
I this case, none of the above applied. The home was relatively new, less than five years old, and had PEX plumbing in good condition. It also had a pressure regulator built into the water supply. The regulators are now required in one of the municipalities that I work in and the plumber's assistant dutifully attached it. However, he forgot to make a simple adjustment to the knob on top.
The buyer was with me, so it took me just a moment to show him how to make the adjustment. Since I do free return visits for my clients, we arranged to adjust it after he took possession. In the end, his low water pressure issue was an easy adjustment rather than a huge potential expense.
PS. For those wondering why I didn't adjust the pressure while I was there, all I can say is that I am a guest in someone's home. I like to leave it the way I found it (unless it is truly dangerous!). It would be like me coming is, deciding I don't like the curtains, and taking them down for ones with little yellow duckies that I like better. As a guest, I should have better manners.