I have done about 6 fasts for weight loss and have perhaps as many more to go. The first was water and some of the later ones "adulterated" with coffee after enjoying several cups of fresh ground stuff to satisfy a craving between fasts. I wanted to try a fast with coffee because I did not want to leave my "comfort zone" at the time. However after a few days I lost some weight, but I didn't feel quite right. The taste of coffee actually became unpleasant.
I then started a water fast, by then the craving for coffee had gone anyway. I felt much better, and was able to sustain the fast for a longer period and with a greater weight loss rate.
You could say starting a fast is like jumping into a swimming pool, you don't want to at first, but after a while the water's lovely. So having weighed up the pros and cons, on future fasts I will stick to water, because after the initial day or so it's easier going and produces quicker results. If I was fasting for detox as opposed to weight loss, I would certainly stick to water.