Unhelpful advice: I wouldn’t trust a “natural flavor” label from any product. They find loopholes to get that label. Just like “cage free chicken eggs” turns out all they have to do is let the chickens out for five minutes a day. If you are in a position to question anything never stay in the grey area. Say no and be safe!
“Natural flavors” is trade-secret manufacturing speak for anything I want that wasn’t created in a laboratory; honey and orange essential oils easily fall under that very broad umbrella term.
If you’re water fasting, your aim is to eliminate things, right? You need to eliminate flavors too if you want to get the full benefits that a water fast affords.
Plain water. Plain seltzer. Unflavored black coffee. Unflavored black or green tea.
Embrace the simplicity.