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. Now, if we take the pure water and now we add some type of additional solute molecule, for example, sodium ions, then we decrease the sommotic potential of that non pure water. So now it becomes more negative. So pure water is given a potential of zero.