If I remember right it was hot AF that day and unless my eyes fooled me, it appeared as if one of the officers had a smile when he got doused. I'm sure it felt good. But that's besides the point. I can see them using any number of other laws already on the book to charge those water throwers with, without having to dredge up new laws. Equipment costs tax payer's money and their portable radios could have gotten ruined, as well as other equipment they might have had on them when exposed to that much water.
Charge them with vandalism, make them pay for damages.