If a seasoning has 3 grams of carb per Table spoon and you add 2 cups water to the dish, does it still equal out to have 3 grams or has it been reduced or weaken down?

3 grams. But nice try though!

The spice still has 3 grams of carb per Tablespoon, but unless you're drinking all 2 cups of liquid that you're dissolving it in you're not getting 3 grams of carb per serving. Let's say that you divide that liquid among six servings. That would work out to 0.5 grams of carb per serving from the liquid with the seasoning in it.
Does that help?