Well, I just tried this...
I even tried just dry shaving first. That did not work so well.
So then I used water with no shave prep. WTG was spotty. ATG removed hair nicely on the cheek but was a little uncomforable. Then I went to the neck. I did a small area but it was too uncomfortable to continue.
I then shampooed and conditioned my beard. I have never used conditioner before. As a head shaver I've never had it around. The other day on a whim I got a bottle to see if it would make a difference in my shaves. Anyhow... Post shampoo and conditioner I tried using just water again. The neck was uncomfortable but not nearly as bad as before. Shaving the cheek that I didn't shave before the shampoo and conditioner was great.
I ended up making some lather to finish my neck and to do my head.
I think I could shave with water only if I really had to.
Fortunately I don't really have to. :)