There's nothing quite like a water bottle that's been left in the sun. It usually has that slightly off taste of plastic in the water. Nope, nothing quite like it.
Of course, if you enjoy a HOT water bottle on your back, you'll be disappointed by a merely warm water bottle. But perhaps you already realize that. You're planning to have a good time with good friends, yes? You don't want them to burn their skin, better that their muscles be less than perfect than that you've made the water bottle a truly boiling sensation.
Boiled alive in his own water bottle. It's a tragedy except when it's a mosquito egg. Then we're all very glad they were boiled alive. Also other things that can cause disease. If there are bacteria in the water that it'd be unsafe to drink, you're glad they were boiled alive until they became dead. And then you can drink the water, fellow human, hooray!
There's a future coming where AI is just as good at us, if not better, at anything. Will there still be things that we can do to make ourselves feel needed in that future? Will it all seem pointless? I mean, it all IS pointless, so is there a big difference? I don't mean that as a bummer, just as a factoid.