Everyone else is focusing on whether the rest of the world uses metric and not that fact that water pressure at a given faucet or shower head will be governed by bernoullis equation which will take 99 things into account such as:

The max height of the water reservoir

The height of your faucet

The design of the pipes leading from the reservoir to your faucet

Air pressure

The pumps in the system

Etc

And the location of the house/apartment. Houses higher up have lower water pressure and in apartment buildings the upper floors have lower pressure than bottom floors. 1bar of pressure lifts water 10 meters high. When constructing heating lines on a new building we might have the heating on on the first 3 floors despite the ends of the pipes leading to upper floors still being open and half of the building missing. The water wont spray out as long as we keep the pressure low enought that it doesn’t rise to where the pipes end.