The M31 waterbottle was made of aluminium covered in felt, some early bottles had a black bakelite cup but this one has an aluminium cup. The bottle is being worn on the right hand side loop of the breadbag. I have been told by a veteran that this was in fact against regulations (presumably stemming from the WW1 breadbag that only had a left hand loop). However, the waterbottle is much more accessible on this side and is almost always seen being worn this way in original photos. The capacity of the bottle is 0.8 litres.