Now, if for some reason we reduce the pressure of water, we reduce the atmospheric pressure, let us say. Then, what happens? When does the water boil? At a lower temperature. So, you can see the vapor pressure and the temperature are very closely related. And if due to any dynamic action of water, anywhere inside water now, if due to flow of water, anywhere the pressure falls below the vapor pressure, then water cannot sustain itself in liquid state. As we have seen it will try to evaporate and come back. So,