Obviously neither of you are engineers.
Between the two of you, you still haven't made it as confusing as it really is yet!
Always bear in mind that static pressure can only be measured when the water is not flowing. This is usually the highest system pressure in gravity-fed systems. As soon as the fluid can flow, the pressure you measure will drop. Slight drop for restricted flow rates, more for free flow. Where you measure the pressure also matters, because the pressure measurement at the nozzle will not be the same a measurement taken a few feet up the penstock pipe.
Rough pipe walls cause pressure drop when the water flows, exactly like wire resistance causes voltage drop when current flows. In fact the analogy between fluid flow and electric flow is so good that you can use a lot of tricks to keep your facts straight, if you know one subject but not much of the other.
Doubling the diameter of a pipe provides 4x the area to flow through for the same pressure drop, just like doubleing the diameter of a wire allows 4x more electric current for the same heat build-up.