I don't know if you guys are talking about the bottle mounts on the forks, or that one on the lower front frame. The one on the frame can get mud kicked on it (though very little since I use fenders in the winter) but I don't keep water in that bottle anyway. I use that mount for a cheap plastic water bottle filled with a spare tube, my multi-tool, some zip ties, and I don't remember what else.

The fork water bottles don't get dirty on my Fargo. It's a good place for them.

He also has the two other mount locations but the frame bag goes there.