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Is your house on a slab? have you tried cleaning out the aerators on the end of the faucet spouts?
I asked about the slab because what you describe can be caused by a leak under the slab. You can confirm this by turning off every faucet/fixture in the house then go to your water meter. If the indicator on the meter moves at all you have a leak. If you can't find the leak then it's probably under the slab. However, it's not clear to me if you have any flow at all anywhere in the house