I think it depends on what kind of tea. Is it the kind that you buy in a can or in the bottles that is sweetened? If so, then yes it can because its basically like drinking soda because they put so much sugar in it. If you make your own at home out of just tea bags and don't put any sugars in it, then it shouldn't dehydrate you because its made of water mostly. I would stick to drinking water to hydrate, and make sure you are getting enough of the other components of electrolytes (potassium and sodium).