So,
my map is leaking, and I don't know why. I have a skybox (not hollow, but that didn't work either) with nothing intersecting it, and for some reason the game treats it as water. (Quite the "leak"!) Brushes with other textures work normally after I place them. Maybe I've just missed something, or maybe the version of Hammer that I'm using for Half-Life 1 is just bad. (Version 3.4, build 1983) I'd be grateful if anyone finds the reason for the leak!
Edit: I forgot to give full downloading permission to everyone who views the Drive document, it's now fixed. I also forgot to mention that Hammer doesn't compile the pointfile.