Brian,
The same letter that refers to the water also says that I need Boost for nutrition. TSA won't let me on with water since I can buy some in the airport, but TSA just about always lets me on with a couple of bottles of Boost, after they read the letter. Once or twice they wanted to test it and I refused to allow it, before a supervisor let me pass. My punishment one time was to be hand searched...which made no sense at all.Another time I brought up the American with Disabilities Act and they let me pass. Most times, however, the TSA person just reads the letter, looks at the Boost and lets me go without a problem.
Unlike many of us who have had to drink nutrition drinks, I still like the taste of Boost and I keep it in my office and in my golf bag for a quick, easy to swallow snack when I feel hungry.

Danny G.