Interesting arguments here, i hadn't pickup up on the strain he seems to be under trying to keep himself "Weightless", from this it seems it might just be very clever cable work and cgi.... And i can't rule it out because who knows what they can and can't do, but the underwater idea seems a little far fetched, just because of the huge amount of crew resources and money needed, it would just be easier to green screen it or something, because by the time you have removed all the water in post i can't imagine there being much useable video left, also between all the various "Astronauts" there is a lot of this well produced video being released every day, so even with their funny money, time would still be an issue trying to edit all these to near perfection and distributed, Unless someone can convince me otherwise, i am going to stand by my theory of a well designed set, with an immense amount of cable work and some clever CGI.
Thanks all who responded