Seriously, if it were me this is what I would do.

1. Do a police report to document the incident in case there is any blowback from further steps.

2. Let it set a few days, not the report, do that soon, and see if he voluntarily fesses. He may have been in serious need of fluid and figured (incorrectly) that you wouldn't mind him borrowing without knowledge. Certainly this is wrong, but better than just plain outright thievery.

3. If he's a tenant and doesn't own up, give him his eviction notice. If he wants to fight it, sign a criminal complaint that will result in a warrant.