I would take them and I always have when I fasted, usually before I have juice fasted though, I only did one 5 day Water Fast but I was incorporating Colon Cleanse products into it which had some sucrose it it as well so I don't know if most people would consider that a water only fast anyways.
I would be too afraid to just do only water alone and I don't know anyone who has done it with only water and not even salt or vitamins or any type of Sugar for more then 3-5 days. Maybe if the person is very overweight they could do it more easily (as the body has a lot more 'food' inside itself to eat if one is overweight) but I have almost no body fat as it is so the most I have ever fasted is 5 days, beyond that I have never been able to do, after that the nervousness and greed for food takes over and I give in.