Barn Owl.
What do you base your comments below on:
They split easily after a couple of outings though.
Can't be relied upon, that's why they're made for recycling after one purchase really.
Although it's a good sentiment and useful in a survival situation.
I am just wondering here if you are talking about your ownpersonal experience, rather than long term knowledge of many users (I'm just curious, as oyu didn't add IMHO or IME etc).
From my own personal use, a fizzy drinks bottle will last three to four four years of use (2-4 days per week), and literally dozens of fellow light weighters that I know, use them for several years with no problems too.
I also have to add, that if they were manufactured for single liquid filling, htis would be marked on the base of the bottle, along with the other info stamped there (this is something marked on drinks bottles for less than continula filling use, as is represented by a number in a mathematical shape).
As someone who had to use '58 water bottles in military service, I will agree that they are OK, but can't see the point of carrying the extra weight, and using something designed to fit in webbing (as I don't use it now). So, although I have quite a few '58 bottles hanging around in cupboards, I tend to stick with fizzy drinks bottles.
I will admit to having one split on its base, but one in over twenty years isn't too back I guess, and is the same number of '58 bottles I have had break on me lol. But, just to add a bit of a twist......The only '58 bottle I would ever use now (and only for teaching), is one of the green ones, as I always preferred them, and they can at least be a talking point (along with their cups too lol).
As for survival situations (and I don't intend to ever be in one lol), Your fizzy drinks bottle with withstand freezing better than a '58 bottle, as well as having the ability to be placed on embers to heat its contents.
Just a few counter points to the 'gear must be heavy military stuff' argument, and also acknowledging that you are much more likely to come across discarded fizzy bottles for bushcraft use than '58 ones.