I'd almost bet money that it's assault if the target decides it is.

Gently putting your hand on someone's shoulder is assault if it's unwanted. Water is less pleasant.

Here's some people on a random website claiming to be lawyers, but also saying the right words: that they can't give specific legal advice and that the OP should not do that and/or get a lawyer. https://www.avvo.com/legal-answers/can-i-be-charged-or-arres...