A leak in the supply pipe.
Lots of stuf can cause it including sediment or a blocked supply line
check for leaks
Friction losses are seldom taken into account which cause drastic pressure drops
water pressure
Low water pressure or cold water main undersized.
With no air in the system anywhere, there would be nothing to hold pressure, so the slightest leak would cause the system to go to zero.
Stopped at all faucets? Didn't pay the water bill. If in cold climate, the line from the outside to probably the water heater has probably frozen.
Possibly a pressure reducing valve installed after piping for first faucet, which would cause situation describing.
If you mean a well tank, the water is forced in by the pump. The residual air pressure pushes the water out to the faucets.
You have to undo the aerator at the end of the faucet and clean the screen or plastic water saver out. It will be plugged with sand or sediment.
Unscrew the aerator from the end of the faucet where the water comes out and clean the screen. Sediment build up slows the flow.
NOPE, actually it will cause more pressuyre drop do to friction losses