Frodo wants to chuck the glass of water into Mount Doom so Sauron can't have it. Galadriel wants it, but restrains herself from taking it from him. Faramir isn't thirsty. Eowyn wants the very best bottle of water, but her bottle of water has been betrothed to another bottle of water for years now (who is giving up her immortality for a bottle of water with an expiration date), so she settles for some slightly less renowned but equally good water (you know all fancy that bottled water is just filtered from the tap anyway).
Lyra has a glass of water that everyone wants to take from her, but she's the only one who can drink it. She spents most of His Dark Materials trying to get back this or that other glass of water, though--at one point her GOW is a person; at another, an object.
I don't even want to start with the Pirates of the Caribbean movies. It's like Musical Glasses of Water up in there; I wasn't sure who had which glass or wanted what water half the time.
Let's see, the most recent movie I saw--Iron Man: Tony Stark wakes up with a glass of water in his chest, and then the bad guy takes it from him (but he has another one, just in case). In the sequel, his glass of water is poisoning him, so he discovers a new one. (No, that's not a spoiler. Yes, Tony Stark dies horribly of water poisoning, no more movies, the end. Right.)
On Lost, most--but not all--of the characters want to get the hell away from the glass of water. They also have a secondary glass of water in their back stories that drives them emotionally, and often a third glass of water in the present. Jack thought his glass of water never loved him, so now half the episodes are about his water issues. Sawyer wants to find the glass of water who caused his parents' death. Kate can't decide which glass of water she likes better. Desmond will travel through time to get to his glass of water. Michael wants to find WAAAAAAATER! Locke clings desperately to the glass of water (DON'T TELL HIM WHAT HE CAN'T DRINK) and wants to make sure he never leaves it (until he's Smokey Locke, at which point all he wants to do is get the hell away from it).
What else... The X-Files: Mulder had a goddamn glass of water taken away when he was a kid that he would NEVER, EVER shut up about, and his search for the glass of water was kind of touching in the first few seasons but after a while he'd say "I HAVE TO FIND MY GLASS OF WATER" and I would be like Oh God, this again, it's one of THOSE episodes and I would mentally check out for the rest of the hour, and I stopped watching after six or seven seasons, but I hear that eventually his glass of water turned into starlight or some shit, I don't even know.
Harry Potter has a shitload of water glasses, now that I think about it--each book is pretty much Harry Potter and the Glass of Water, although, on a larger level, the entire series is about him trying to stop Lord Glassofwater from taking over the world. The last book is pretty much a whole cabinet full of water glasses, honestly. Collect them all!
Edward loves his glass of water, but he must never, ever drink it. Bella really, REALLY wants him to drink the glass of water. Eighty percent of the books are the two of them arguing about drinking water, with Bella splashing at him occasionally. Jacob also wants to drink the glass of water, but Edward ends up with it instead, and then he and Bella have a little cup of water of their own (nooooo don't take their cup of water!), and Jacob will get to drink that.
I'm going to stop now, because I feel kind of dizzy.
So basically, if you're a writer, the question you need to sit down and ask yourself is: what are you going to do with your glass of water?
ETA: A little followup you may want to read about how this is an editorial tool, not a writing philosophy.