Describe precisely what is wrong physically in the famous escher drawing

The work is Waterfall. The lithograph was first printed in October 1961 by Maurits Cornelis Escher (1898-1972).

This work consists of rectangular beams that overlap perpendicularly. If we follow all parts of this construction with our eyes, no single mistake can be discovered. However, it is an impossible whole because suddenly there are changes in the interpretation of the distance between our eyes and the object. In the drawing this impossible triangle was applied three times. Water from a waterfall sets the wheel of a mill in motion and then runs downward, down a sloping gutter between two towers, slowly zigzagging to the point where the waterfall begins again. The miller must occasionally pour a bucket of water to compensate for the loss by evaporation. Both towers are of the same height, but the one on the right is nonetheless a lower floor than the one on the left.