And all these water molecules are continually colliding with the cell membrane. And because we have such a high number of water molecules, some of them are likely to actually pass across when they collide. So we see that water is the great exception to the rule above. Water molecules can cross bilayer membranes with relative ease, 1 billion times more likely than these ions or these ions. So now, this is because they do not contain a full charge. There is a very high concentration of water outside and inside the cell.