[pcai]

Just buy 2 of the 0.33L! You already did the math!

[wst_]

I assume it's a can. No go for me. Not sure about OP. The convenience of half litre bottle is that it's relatively small and you can keep it closed.

[jorvi]

Yep, exactly this. You can sip from a bottle and put it back in your backpack. A can you have to leave outside the backpack once opened.