I make decaf tea with liquid saccharin. I think I've read that the liquid version of sweeteners can be counted as zero carbs unlike the powder packets. As long as I make sure to add just a few drops of sweetener to a mug, this tea is pretty good! (If I add too much it starts tasting bitter.)

The question is, can I count this drink as part of my water? I drink about a gallon of water a day, but I do have to force myself sometimes to drink when I don't really want to. But, I can sip this tea all day long.

Even tea does contain a small amount of carbs (sorry). If you are drinking a gallon of water a day this is enough. Water is water however and most people here would say you can't count tea as water. Others would say it's the total amount of liquids which is important.
Green tea is healthier than black by the way.