If water is scarce, then neither caffeinated coffee or tea or hot chocolate are entirely appropriate physiologically since they are all mild diuretics (emphasis on mild in moderate quantities). OTOH, the morale boost and/or pick-me-up and/or warming from the drink can be worth a lot to a survivor. Like with everything, you have to use a little common sense, balance the pros and cons, and do what's best for the particular situation in which you find yourself. Like anything in your survival kit, they are a tool. One to be used when and as appropriate, no different than any other tool. And, water isn't always scarce, either.