As bad as it sounds, it's not uncommon to drown vermin in cages. Yes, it's not the most humane way of dealing with them, but if you're living on a farm and trap an animal in a cage, you basically have three options:
1.) Let it go
2.) Kill it on the spot
3.) Let it starve
For pests like raccoons, #1 isn't an option unless you're willing to drive off your property and let it go somewhere else (and even then, you're just moving the problem to someone else's property). If you want to dispose of it right away, it's harder than it sounds to cleanly put a bullet in it since they're usually flailing around. So you risk both damaging your cage and not finishing it off cleanly if you try to shoot it while it's still in the cage. In this case, it's usually the most expedient (and arguably most humane given the circumstances) to drop it in a barrel of water until it drowns. And for obvious reasons, you probably wouldn't want to do #3 unless you just didn't realize it was captured or forgot about it somehow.
I know I'll probably get horrified or autistic stickers for this, but these are the kinds of things a lot of people wouldn't know or think about unless you've had to deal with pests in a rural area.