Hi There, I am trying to understand if I have a vacuum in the below scenario or simply just really low pressure. A pump supplies a pipe with a constant supply of water at one end (Point A) the water discharges several kilometers away at some lower elevation (Point B). At "Point A" a valve closes and seals. I assume that the water level in the pipe begins to drop, however, at some point it stops. At this instance have I created a Vacuum at point A? Or is the pressure at Point A simply below atmospheric pressure but above 0 pressure (by some small amount) due to the pressure created by water vapor? The Engineering side of me sees the pipe as a cylinder and the fluid level acting as a piston, and as the piston lowers it creates a vacuum in the pipe, but I feel as if this is a poor way to look at the situation.