The Japanese metaphor "水も滴る" (mizu mo shitataru) is part of a longer phrase "水も滴るいい女" (mizu mo shitataru ii onna), which literally means "a woman so beautiful that even water droplets shine or fall from her."
When used in context, this metaphor describes a woman who is so stunning and beautiful that she causes even the water droplets to drop, as if they, too, are drawn by her beauty or are condensing due to her cool and refreshing presence. The implication may be that her beauty is so potent that it affects her surroundings.
In a broader sense, the metaphor could be used to appreciate someone's attractiveness or charm that is so strong it can influence the environment or the people around them.