And one important function of the kidneys is to basically reabsorb as much water as possible. And this must take place very quickly. In fact, if we examine the cells found within or next to the lumen of the collecting duct, we'll see that these cells express a high concentration of these aquaporean channels. And these aquaphorn channels are used to basically reabsorb as much water as possible back into the capillary. So the water moves from the high concentration to the low concentration. And again, just like any channel, these aquaphorns don't actually use energy ATP molecules.