Do I need to apply corrections for changes in atmospheric (barometric) pressure?

Answer: The VW piezometer is a sealed unit that is sensitive to any pressure on its diaphragm. It does not distinguish between pressure of the atmosphere and pressure of the water. It responds to both. However, whether this is important or not depends on your application.

Suppose you suspend the piezometer in a standpipe or water well that is open to atmosphere. The piezometer will report the combined pressure of the water and the atmosphere above the water. If your intention is to monitor the level of water in the well, you must correct for variations in atmospheric pressure.

Now suppose you seal the piezometer in a borehole to monitor pore-water pressure. In this case, the pressure acting on the diaphragm is only the water pressure at that depth. Thus you would probably not correct for variations in atmospheric pressure, even if you later found a relation between atmospheric pressure and pore-water pressure.

You can find more about this subject and how to use barometer readings to make corrections in the VW piezometer manual.