I know that we are supposed to stay away from fruit, but lemons and limes I think are the exceptions. Neither lemon or lime juice contain any sugar/carbs whatsoever. You can look on the back of a bottle of REALEMON or REALIME to see for yourself.
Also, you can purchase unsweetened cranberry juice concentrate at your local health food store. It naturally has no carbs. in it also. It's great in aiding digestion as well as maintaining the urinary tract and kidneys. You can put a Tblsp. in a eight oz.
class or water and drink. You could even sweeten it a little by using stevia (also found in the health food store)
I hope this helps!