Plane travel and formula

I’m going on a trip soon that will involve 2 flights with my 6 month old. It’s a total of about 10 hrs. I’m supplementing with formula and he will only take his bottles warm/hot. I use powdered formula and will need to mix up small bottles. Usually I bring hot water in a thermos with me on outings. What should I do? One article says you can bring a reasonable amount of water on a plane for your baby, but I don’t know if they will look down on my thermos of hot water. I can afford for them to confiscate my thermos. And I don’t know what the regulations will be on my return flight since it’s international. Any suggestions? What have you mommies done that worked?