Just saying but what would happen if you broke one of the windows?
Not much, really. Close up the access point, and the water would all disappear in short order. If you didn't close it? Well it really depends where. But unless you did it in the forge where there's that open lava, probably not a lot, really.. water prefers to drop straight down, and can flow 7 squares horizontally from any landing point. But the water level never rises from the landing point.. so it can't "fill up" a room.
So, crack a block on the bottom floor and you'd have a wet floor. The rest would be perfectly fine. Crack a block on the top floor, and you might have a bit of a mess as it flowed downward over stairs and through ladder shafts but nothing too serious.
Now in the forge? Well.. lave + water = cobblestone, so you could end up stoneblocking a good portion of the room. That'd be an ugly mess to clean.