the pressure on ur maintap is usually 4 bar, it is impossible to increase the flow rate, of water coming in, the flow rate that you fill ur tanks up with, all depends on which tap you are filling from, a lot of outside taps the pressure is no good as the pipe work going to it is thinner that 15 mm and wont carry enough water, to fill quickly u might have to get an attachment to your main cold tap in the kitchen, (this usually has the best pressure) if you live in a new build house, the pressure should be ok all around the house,, the flow rate at the di might be set and there might be nothing that you can do about it, as too fast might not work properly