The gravity systems in this case are not pressurized. They just have a water tank in the loft/airing cupboard and the hight of the tank determines the pressure. 0.1 bar for every 1 meter height. You open the faucet and gravity pushes out the water.

Its a nightmare, I used to live in UK and these systems are barely enough for anything really.

In europe they mostly use Bars as the unit of measurement.

Mostly water pressure is around 1-2 bars as a minimum, but there are still places using different standards, for example the old style gravity-fed UK watersystems with sub 1 bar pressure, but those are not very common anymore.

Most domestic sanitary products in the EU are designed to be used on 1-5 bar pressure.

I read somewhere the domestic water pressure to be between 4-6 bar, however not sure how realistic it is accross the whole EU and also what you got at the mains and what you got when opening the faucet is two different numbers.