Same! Sadly, I can only tolerate one brand of water. 
Stupidly, I relocated to FL (for fam) and it's close to impossible get that brand  here. I don't fly anymore. Even with a note from my doctor, I wasn't allowed to bring an unopened bottle of water on the plane. 
I have less than 5 safe foods & my allergist/immunologist told me two weeks ago, she has no more suggestions to help me.  Another one said the same thing in 2016. F MCAS!! I'm sorry 🥹