When you say taps have come loose, Do you mean the knob/handle or the body of the tap.
The body will have flange under which fits a rubber washer that creates a seal, On the underside there should be a plastic washer before the nut is screwed on. Sounds as though the nut may just need tightening a little but don't over do it.
If you mean the knobs/handles and the screws ( approx 4mm) have worked loose then you need to apply 'loctite' to prevent it from happening again.
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