The assist could be simple pressure. That's how water comes out of your faucet in a 2nd-floor bathroom. The pressure might be from pumps, but it could also come from a passive system with a high water tower. Substitute the tower with some nearby mountain with a small lake on top, and there you go.
If it's pressure, why did the water bore thru solid rock (which is the foundation of teh city - you can see it by circling the circumference of the town on foot), and not emerge somewhere in the lower tundra?
And for all of you who keep saying "it's a fantasy game, it doesn't have to make sense" - sure, that's true. BUT: without a proper touch of realism, any game becomes uninteresting, because it loses it's ability to captivate the player and have him/her immerse themselves in the environment. Thus, when seeing something that doesn't make sense, it draws attention & curiosity, and stimulates the impulse to investigate.