When my sister was foster cats, she let them drink out of her glass. And no she didn’t change glasses. And yes, my sister is weird.
And yet Hermione, who is an utter doofus, has figured out since that it’s not okay.
Given that cats tend to be a bit dehydrated in general, according to the current wisdom, allowing them to drink out of whatever vessel they prefer is a good idea. Despite the abundance of water bowls in my house for the dogs that the cats can share and also a couple that are cat only, my cat would prefer, it seems to drink from the dripping bath tap.
Cats are weird. They are not all masters of grace as has been portrayed in literature. Some of them are clumsy, delightful oafs.
It’s your girlfriend’s fault that the cat knocked over her water glass, because it is never the cat’s fault, but I doubt you will be able to convince her of that.
It’s the cat’s fault. Everything is the cat’s fault. Broken vase? - cat did it. Scratch on the coffee table? - cat did it. Upset laundry basket? - cat did it.
Hey, if the cats don’t want the blame, they should learn to talk. Thanks, cats, for keeping me out of trouble all these years.
Who the hell gives their cat water in a glass? Not the cat’s fault at all.
In the words of Marcie “Married with Children” Rhodes,
If you give a chimp a gun, you don’t blame the chimp if it shoots someone
Well, apparently the OP’s GF does.
In our case, the cats just took advantage of any glass that was momentarily unwatched, and then it got to the point where we just kept a couple of glasses around in addition to their water bowls, especially since Shadow likes to cultivate bladder infections. However, we got one of those cat water fountains, and keep it full in addition to a regular water bowl, and the cats are delighted with it. They still drink from the regular bowl, but they drink a lot more water from the fountain. Plus they enjoy watching it.
This. I have a hard time saying an animal is ‘at fault’, ever. Sometimes they will do stuff that they’ve been specifically trained not to, and then quick and appropriate consequences are in order, but ‘blame’ really doesn’t come into it.
I knew a cat whose face was entirely too fat to get into the tall glasses that his family used, so he learned to knock glasses over to get at their contents. He particularly liked milk. We learned to keep a sharp eye out for ‘the paw’ around that one!
Bad smell in the house? Cat did it! 
Dude, you think that’s bad?
My wife often leaves for work and locks the basement door - where the cat’s litter box is.
Yet it’s the cat’s fault for shitting in the corner :rolleyes:
One of our cats likes to steal straws. When we drink something with ice in it we’ll usually use a straw, and along will come Cory and steal the straw and run off with it. We can’t really get mad at him for it, so we just laugh. It can be annoying though. Especially since maybe 1 in 10 times he does it, he knocks over the glass in the process.
Oh my god, what the fuck?? What is your wife thinking?? We were so lucky when we got this rental house. Both doors down in the basement–the one into the rec-room like area and the one into the laundry room–have the corners cut out of the bottom of the door, specifically so the cats can get through even if the door is closed. The owner (our landlord) had cats, too.
Belive me we got into a “heated discussion” when I found her chasing the cat around the house with a slipper and I asked her “What the FUCK did you think was going to happen?!”
Or put it in coffee travel mugs like I do.
Or use bottled water (get a good quality water bottle at a convenience store or gas station… not one of those ultra flimsy ones with the tiny twist off top) and refill it at home when it’s empty. A closed water bottle doesn’t spill and make a mess 
Of course if you’re drinking something other than water that’s not as good a solution.