besides the small one that is outside the membrane area, all but two pass the membrane. The
ends of those two face each other which means that the helix dipoles
face each other, and that helps with the specificity for water passing through aquaporin, and
not other molecules (but this is one of the topics of the SFB course (MOL066 at the RU).
If you let the students load the file AQUA_water.pdb, they see the water molecules too, and can see the stations a water molecule passes when going through (some phylosophy: Since waters are seen at those spots, they like it there better than at other positions. So on their way through, they probably jump from point to point, the points being the positions where you see waters in this static picture.