What does the dotted line between thge water molecules represent

dotted line = not a complete bond / a broken bond

Explanation:

well, first we have to start with the types of lines.

there are 3 types: solid, wavy, and dotted.

the solid means that there is a fixed bond, and we know much about the bond and its stereochemistry

the wavy means that the bond is fixed, but that we dont know much about its stereochemistry

the dotted line means that we know about the bond's stereochemitry, but it is either a weak bond, a broken bond, or an incomplete/partial bond. for eg: a hydrogen bond