Shower power -- I can get a more effective rinse by removing a flow restrictor. Have I increased water pressure? What principles apply here? I watch a plumber on social media; he explains how to do simple fixes. Sometimes his customers want more "pressure" coming from the shower head; when they feel like it's just a "trickle" -- they can't get the shampoo out of their hair. So he removes the flow restrictor and customers are so happy. His video is headlined something like "How to increase pressure in your shower". Other plumbers comment that he is an idiot: by increasing the flow, he's actually DECREASING the pressure, which is what they learned in fluid dynamics class. But the shower user experiences what feels like increased pressure on the skin. How can this be explained in a scientifically accurate way?  Thank you! (I'm his mom and I'm a retired high school science teacher.)
 A: Here is a way to think about this which might help.
A plumbing system can be thought of as a source of water pressure which establishes a  flow rate through some constriction or pinch point contained in that pipe. More constriction means less flow, and less restriction means more flow.
This picture becomes complicated by the presence of two constrictions in the flow, one right after the other. In this case, the flow will be established primarily by whichever happens to be the more restrictive of the two constrictions.
The two constrictions here are the flow restrictor in the neck of the shower head, followed by the spray nozzle array from which the water exits. If the shower head nozzles are more restrictive in total than the flow restrictor upstream, then you'll have significant pressure available right behind the nozzles to propel the water forcibly enough to yield a good spray pattern.
But if the flow restrictor is instead choking the flow more than the spray head, then you get a dribbly spray.
This picture is complicated by the fact that most shower heads behave as convergent nozzles in which the water flowing into the shower head is accelerated as it enters and flows through the nozzle openings. this makes the exit velocity dependent on the  flow rate through the system as a whole: low flow rate means low exit velocity and high flow rate means high exit velocity.
It is worth experimenting around with different shower head designs which are restrictive enough to limit the flow rate yet still accelerate the flow through the nozzles enough to get a strong spray hitting your skin. This is a better solution than inserting flow restrictors upstream of the nozzle array.
