Unlike with the newspaper one, this is definitely a change I would 100% support. We all have different opinions on the environment I am sure we have all realised that by now so I respect everyone else's opinion on it, but my take on it is that just because you are doing one bad thing for it (flying a plane) doesn't mean it isn't also a good thing to making smaller changes (removing plastic water bottles).
I have just recently gone mostly vegetarian (at home I eat vegetarian and I will choose vegetarian dishes but if I am offered meat by others or I am in a different culture that is meat heavy I won't say no). That is a much bigger change than just bringing my own water bottle. Fairly certain I can handle that "sacrifice" if I can go vegetarian.