Domestic mains pressure depends on where you live how many houses it has to serve and how tall the buildings are. Example on a main road in London you would expect the main pressure to be 10 bar or so, but in very remote places you should expect low pressure e.g. in the lake district where there is very little housing for miles apart. You Should expect about 3 bar pressure in some remote areas. Most domestic taps and boilers can run off 1 bar pressure, but if you had a house three stories high then this would not be enough pressure and your water will come out at a drisel or not at all on the top floor. 10 bar mains pressure is pretty standard now. Just imagine all your neighbours getting up at 7 in the morning all wanting a shower at the same time? That is a large demand on supply! You may even notice that a some parts of the day you have better pressure than other times of the day depending on the demand on the supply.