Single cavity tracing. Bottom: Volume plot of a single cavity traced over 72 time steps. The point color highlights whether two (red) or three (blue) water molecules are contained in the cavity. The labeling of the y-axis gives the volume numbers as well as the corresponding water molecules that would approximately fit into the volume, where the volume of a water molecule is approximated by 30 Å3. Top: The two images on top of the graph show the traced cavity (red) for two selected time steps together with the contained water molecules. In the right image, it can be seen that the traced cavity has split. A second, smaller cavity (yellow) contains the third water molecule.