The answer to your question depends on who you ask. LOL It also depends on whose rules you're following. From a liquid only perspective decaf tea would be counted. From an Atkins standpoint, though... just water is water. If you're following Atkins, all "can I have" questions can be answered on the food lists. There's one for Induction... and another when you transition to OWL.
From the Induction list, regarding water:
Water – at least 8 eight ounce glasses per day including…
I am the master of my fate:
I am the captain of my soul.