Baz, im not sure if you are deliberately misunderstanding or what. Most people (i think!) who normally drink say 8 glasses of liquid a day, arent going to suddenly be drinking 16 glasses because they diluted their juice by half.
In your example if a glass of aple juice had 3 spoons of sugar, you wouldnt be able to add water to it as it's already a glass full f apple juice. but if you diluted it to 50% with water, and still drank a glass of drink, you'd have halved your sugar. As i said i didnt see the prog, but i doubt they were suggesting that water somehow manages to make the sugar in juice disappear!