Uhhhh...if you are dead set on doing exercise along with being on your feet so often at work, I would say that a water-only fast would not be practical for you. While I personally choose to water-fast only, I also make sure that my exercise levels and work-on-feet time is drastically lower than usual.
It sounds like a juice fast with mixed in days of water only (most likely your days off from work) will be your best option.