About 8 years ago I had about 5 detox foot baths.
Each one produced a lighter shad of "gunk."
The business moved and I recently thought I would like to have a few more treatments. This morning I sat for 30 minutes and the water remained clear!
Actually, I was disappointed. I guess I should be happy, but the expectation of getting rid of toxins was not achieved.
To answer the question if the water changes color even if your feet on not in it....don't think so!
Machine would have to be pretty dirty to leach the muddy colors into the water.