Tony Bryer wrote:
Is there a rule of thumb as to the likely static mains water pressu
I'm about to install an Ariston undersink heater which needs a
pressure reducing valve if the pressure is more than 3.5 bar. The
Thames Water site is one of those that has been expensively designed
with not too much thought for what users might want to know.

It can vary a lot. Mine is 6 bar and I have to use such a valve on the feed
to my water softener.
3.5 bar I can hold back with my finger on the tap. 5 bar I cannot