There are two types of piezometers in common use today: standpipe piezometers and diaphragm piezometers (VW or pneumatic). There is no need to saturate standpipe filter tips. Water flows into them easily. VW and pneumatic piezometers do not require saturation either, but there is some air in front of the diaphragm that should be displaced, as explained below:
Diaphragm piezometers, whether VW or pneumatic, contain air between the diaphragm and the filter. For best results, you should displace this air with water. VW piezometers have a removable filter. Pull on the knurled ring to remove the filter. Fill the cavity with water and then replace the filter. Pneumatic piezometers don’t have a removable filter. In this case, you simply direct a slow stream of water into the piezometer or submerge it in a bucket of water and tap the bubbles out.
Some people install the VW piezometer with its filter end up, and our instructions for grouting-in piezometers use this technique. This generally isn’t possible with a pneumatic piezo, since tubing is so stiff. In any case, not much water will drain out of the piezometer so long as it isn’t knocked about during installation.
What happens if there is a small bubble of air? The air will slow the response of the piezo, since the air bubble must deform before it can transmit the pressure of the water. More water must flow into the piezometer to make that happen. Eventually, the air bubble reaches equilibrium and transmits the full pressure of the water. If there is plenty of water available, the slowed response is unlikely to cause much of a problem, and over time the air bubble will disappear. If the piezometer is installed in a low-permeability soil, where less water is available, this process will take longer.