That depend where the pressure is dropping. Possibly a plugged valve under the sing where pressure loss is seen, or possibly a leak under the floor, especially if piped with Poly-B.
Sounds like a bad/failed water pressure regulator.
It is the weight of the water pressing down from above. The greater the depth the greater the pressure.
Defective bladder / low pressure inside the tank
it causes a decrease in atmosperic pressure A+
Expansion of the water inside due to heat causes the system to be pressurised.
entry of water that causes turgor pressure in vacuoles of plants
Something is wrong in your pressure tank, possibly waterlogged and rusting.
Changes in temperature and pressure.
Water pressure.
Increased heat or reduced pressure or both.
A wall cloud marks an area of low pressure within a mesocyclone. The pressure drop causes a temperature drop, which in turn causes water vapr to condense.
low/poor water pressure coming from the utilities/street