That fuel can looks like a wedco...they are very good cans in my opinion I have eight of them myself, 6 fuel 2 water. When you buy them new you can order the spout as well,it clamps on. If you buy that one and they dont have a spout you can get them at expedition exchange. Wedco cans are metal just so you know.
I'm not sure they are fuel cans as I have one that came with my unimog when I bought it. Mine has a white lining and a red "rubber" seal in it. I also have bought 2 fuel cans with the normal size/shaped spout on them and the lining is a reddish color with black rubber(viton) seals. The 2 fuel cans also have FEUERGEFAHRLICH (?) on them and my other one does not. I have a swiss unimog and the 2 fuel cans are swiss also. I can only guess as to the original owner of the can that came with it. I'll have to guess Swiss as they(unimog's) come with one from most importers. I'm no expert on the subject but everyone has to drink and I don't see any other style of water cans for sale on the surplus market. Look at sceptre they make a fuel and water can. Even the old metal military fuel and water can. The metal water can is alot less prevalent on the market than the fuel can is. I'm not too sure I would order them for a water can, if that is what they are.