That would be stressing the body, when the water only fast is itself a method that is complete, along with rest.
You would also be depleting minerals, through the exertion, and that would tend to throw off the electrolyte balance, which is handled quite well, usually, if the Water Fast is left alone to do its work.
However, if you were doing a coconut water fast, you might try the Bikram...
But it probably bears repeating, that anything besides water is really going off-topic to the intent and value of the water-only.(forum, that is.)