Thanks for all the input, everybody!
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I don’t see any issue with it since you could just check the book out and drink with it at home. I could see being more stringent around the rare books or maps departments or at the computers.
The first two, yeah, but how likely is someone to damage an expensive part of a computer in a spill? I’d think that the keyboard or maybe the mouse would take the brunt, and those are probably the cheapest things in the library. (I got my current mouse for something like $3, and I don’t buy them by the gross from a computer manufacturer who’s probably ecstatic that I recently bought a thousand of their computers.)
ETA: Come to think of it, my university’s flat-rate book replacement fee ($150) probably wasn’t that far off from the unit cost of one of the libraries’ no-frills bought-by-the-ton desktop computers.
Well, the water fountain at my library does, in fact, taste kind of yucky. I bring in my own tap water from my own house, which tastes better.
I don’t know about the library at my campus, but the writing center does not allow any food, drink, or even gum anywhere within its confines.
The main research library at my undergraduate school used to have a lounge where you could buy coffee, albeit vending machine brew that was undoubtedly horrible by today’s standards. Still, being situated in a corner of the widest floor, the room offered a dramatic view and smoking was allowed. It made for a nice study break.
My first university started allowing food and drinks into the library sometime during my years there - before the change, people would simply just go study at one of the 27543 Tim Horton’s and other coffee shops in town, where coffee, doughnuts, bagels, sandwiches, etc were easily and cheaply available. When the school put a café into the library, more students started going back there, and the library made money by charging 2-3 times as much for the same or inferior stuff.
Who said university students were smart? 
Also, there was the constant frustration at losing your desk/study carrel whenever you wanted to go get something to eat or drink, because you couldn’t leave it in the library without risking theft or people simply dumping your stuff on the floor. Having food and drink services on-site let students stay in the building longer.