There is a fair amount of adhesive/glue that is on the flat side of the canteen. If you paint it, that won't matter, however, if you stain the canteen the stain will not be absorbed evenly and will show light areas where the glue was over applied.
I bought this wooden canteen for my persona civilian militia outfit. I am very pleased how well this product is made. It is just what I needed to fill the appearance I want to portray. Having the canteen in natural wood color provides the option to stain if desired. I also appreciated the rapid replies by Samson to my questions. I am satisfied to have made my purchase with them.