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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...

It may be simple battery (the usual standard is “harmful or offensive touching”, without a legal excuse, including by causing any object to do that.

https://www.sfgate.com/bayarea/article/sf-man-sprayed-unhous...

There's an article from San Francisco about a man being charged after hosing down a homeless woman. Ultimately the charges were dropped, but the answer to your question is yes with caveats.