i myself have gone longer than the three days (like 4) on water.
i dont know how you do it that long. its amazing! it is safer with the juice. like you dont have to worry at all about getting sick and stuff.especially if you are doing a lot of activity.
i think water is cool if you take it easy and know the warning signs of when to break or when you might need some juice for electrolytes. the lemon juice drops is a good idea. maybe i will try a Water Fast with that.