Hey Michiel,
The second waterbottle is no doubt German, pre war aluminum construction, one would need to remove the cover to be sure, as a german waterbottle will be marked, the covers on the Belgian waterbottles had the snap opening in the center of the flat part of the bottle, rather than the side like this one, and Belgian bottles are seldome marked.
Best wishes
Gsu
The second waterbottle is no doubt German, pre war aluminum construction, one would need to remove the cover to be sure, as a german waterbottle will be marked, the covers on the Belgian waterbottles had the snap opening in the center of the flat part of the bottle, rather than the side like this one, and Belgian bottles are seldome marked.
Best wishes
Gsu