That was weird, I enabled the "VET" mode on the cat flap, since Talisker is going for a checkup this morning, and this stops him from getting out and disappearing for hours. After he'd eaten some of his breakfast I guess he wanted a drink, and since he couldn't go out using the cat flap, was forced to drink from his bowl.
First he "scraped" in front of the bowl using his front paws, then he actually dipped his front paw in the water, and licked it off a couple of times. After that, he drank from the bowl as normal.
I decided to give in to him, and let him outside anyway (it's several hours before the vet), and he wandered off for a few minutes, presumably to find a puddle to drink from.