Water weight is talked about because we are actually more than HALF water ourselves!!! Water is in our muscles and our fat and our organs... everywhere.
It's hard to recognize fat weight/loss on a scale because our water weight fluctuations are much bigger than fat fluctuations. See the sticky about it here:
http://www.3fatchicks.com/forum/weig...er-weight.html
When we lose weight we lose fat and water and lean mass (muscle). So when you get on a scale how can you tell how much you lost of each? You can't.
But we do know that to lose fat, we have to create a calorie deficit. As long as you're doing that consistently, the scale will move down, and some of that loss will be fat loss.
So, you can't worry about "water weight gains" from drinking tea -- enjoy the tea! It can help you lose weight if it helps you feel full and not eat other foods. Keep the calories down, and the fat losses will grow.
As for how much is too much, that varies by person and situation, but several cups of tea, a coffee and a diet coke are nothing to worry about... The people having problems with too much liquid are usually drinking gallons of liquid a day.