You should have some salts to keep well hydrated, also be healthy and don’t have any problems like diabetes, or with your kidneys. Anything over 36-48 hours would be better to check with a doctor first.
The only times I've got dizzy when '24h water fasting' are when I've been eating normal/high amounts of carbs in my diet around the fasts.
I've been doing a few days/week of 24h water fasts again, but on a very-low-carb diet, and can report no dizziness whatsoever.
An additional benefit (also mentioned by others) is that I don't have any insatiable hunger pangs on the water fasts (which I did when I attempted them on a normal/high carb diet).