So objects naturally move down their gravitational potential gradient from a high potential to a low potential. Now, in the same analogous way, if we take a water molecule, the water molecule will always move down its water potential gradient, also known as the zmodic potential gradient. So water naturally moves from a high osmotic potential to a low asthmatic potential. Now, when an object, a mass, is on the ground, we define the ground to be a zero potential. And in the same exact way, we give pure water a value of zero asthmonic potential. So pure water is arbitrarily assigned an Astronic potential of zero.