A water idea
 

I went through security in San Francisco last week and they did allow an empty water bottle. I took the lid off the water bottle and took it out of my backpack going through security. When I got to the gate, I filled the bottle with water and finished drinking it before I boarded the plane.

I might start flying with a large coffee cup. I can have the flight attendant fill it with water and while I am at the airport, I can fill it with water from the drinking fountain.

On the flight when they came by with drinks, I asked for tomato juice and water. They gave me a look like I was pushing the limit, but those water glasses are rather small.

Or you can bring a ziplock and fill it with water :))

They asked the man sitting near me if he wanted two glasses of water. If they give you a can of soda or juice, it really is two or three glasses.

Tomato juice and water? Those are non-alcoholic! :p

Well, TJ and water would be a mixed drink, so maybe it is more natural for some people to order that instead of straight TJ. Or you could ask for TJ with a water chaser, which also would be like ordering a real drink.

Here is another option:
http://wingsworldwide.com/tfclin.htm