Occasionally, students become confused when thinking about osmosis and osmotic pressure because, contrary to the everyday meaning of language, water does not flow during osmosis from regions of higher osmotic pressure to regions of lower pressure. Rather, water diffuses from regions of higher solvent activity to regions of lower activity and this flow produces a pressure. Not vice-versa! Plant biologists minimize this conceptual confusion by viewing osmosis in a different manner.
When water moves from one compartment to another in our simulations, it does work and consequently has potential energy. Plant biologists have coined the term water potential (psi) to describe this energy, and they define osmosis as the movement of water from regions of higher potential (activity) to regions of lower potential (activity). Equilibrium between two compartments is reached when their water potentials are equal.
By convention, the water potential of distilled water is zero and it becomes more negative as solutions become more concentrated. Thus, net diffusion of water occurs from regions of less negative potential to ones of more negative (or lower) potential and continues until the potentials become equal. This way of visualizing osmosis eliminates confusion for many because water potential is more closely related to the behavior of water than is the concept of pressure. For this reasons, we've also used this thermodynamic view of water activity and potential energy in our presentation.
Osmotic pressure is still a useful concept, however, especially when the differential movement of water is related to other hydraulic phenomena such as arteriole pressure (in the physiology of kidneys) and to the use of reverse osmosis for desalinating sea water, using hydraulic pressure to "create" distilled water from a saline solution through a selectively permeable membrane.