I have had a similar problem. It was found out that there were some small rubber seals behind the taps which were fucked.

You should check that out - However, as you have bad pressure through the entire house, and not just one or two areas, it may be something worse.

How old is the system?

Have you tried turning off all your water outlets, and then go look at your meter to see if there is water leak somewhere?

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Should have bought an STI