The simple choice of drinking mineral water over sugary beverages or tea would certainly do wonders for your body, especially if you always choose water over anything else.
As to whether or not this would work, well, it’s kind of odd you posted this because I love water and almost always drink it over anything else and I also sleep without a blanket, with only boxers, and my ceiling fan on! (even during the Winter! )
I call it comfortable… and my parents call it stupidity!
Who knows? Maybe my love for water is to blame for my cold resilience (although it could just be a coincidence…)