When I ride my bicycle I often drink a lot of water because I get thirsty and like to keep hydrated, my bicycle can only fit a single bottle holder because the front derailleur is mounted in such a way to prohibit a second bottle cage from being mounted, so therefore I can only take a single bottle with me.
My friend has enough space for two bottles, but I feel extremely rude if I ask him if I'm allowed some of his second water because he has done the hard work of carrying it all the way and I am just going to drink it without repaying him in any way.
How can I ask my friend if I'm allowed some of his water without getting into an argument or offending him, should I offer to carry some of his stuff in my jersey pocket so he has less weight on him on the way back?