Hi guys…
I’m traveling soon with my baby, and I’m concerned about getting through TSA and airport security with his water thermos. He only drinks warm formula, so I need to bring water at the perfect temperature for him. The amount will definitely exceed the 3oz limit since we have a 7-hour travel day.
What’s the best way to handle this at security? Will they allow me to bring a larger amount of water for my baby, and if so, do I need to take any specific steps or provide any documentation? 
Leave your bottle empty and have a restaurant or coffee shop fill it up after you pass through security.
We get the thermos filled with very hot water and a separate bottle with cold water. Then, we mix the two to get the right temperature, which essentially doubles the amount of water we have instead of just having it at drinking temperature.
Another tip is to bring 3-4 medium bottles with formula powder instead of the usual full bottles. This way, you can offer a bottle at different times like in the terminal, during takeoff, and mid-flight, ensuring you always have one ready. Sometimes, we also carry extra powder just in case.
Just let the TSA agents know you have clean water for an infant’s food, and they usually won’t be bothered. We went through several major airports with about a gallon of ready-to-feed formula and 60 oz of clean water, plus powdered formula. They just checked my bags manually, did a vapor test of the water (I opened the thermos, they held a vapor strip above it but not touching, and nothing showed up, which is good).
This added about 5-10 minutes to our security process. The toughest part was flying out alone with the baby. I couldn’t go through the X-ray machine while holding her and wasn’t sure when my husband would get to TSA (he was parking the car and checking the bags), so I had to go through a pat down. 
The baby kept trying to play with the TSA agents, which made everyone laugh.