Stephen,

Use beeswax if you re-line your canteen. That was what was originally used. Me, if I'm gonna drink from a canteen at a reenactment, I cheat, LOL, I use a stainless steel one and If I use a wooden canteen, it's lined with food grade plastic. LOL. As much as I like to be authentic, I consider health issues more important. Drinking from tin is a bit chancy. I do have authentic canteens, but they are for show, not use.

Len