Here's why:

* Water potential is the tendency of water to move from one area to another. It's influenced by factors like pressure, solute concentration, and gravity.

* Pure water has the highest water potential because it has no solutes and is under no pressure (except for atmospheric pressure). This means there are no factors hindering the movement of water molecules, and they are free to move from areas of high concentration to areas of low concentration.

Important Note: The water potential of pure water is assigned a value of 0. Any other solution will have a water potential value less than 0.