I had prior experience doing such a diet once before (for 21 days a year earlier) knowing 8 weeks could be realistic for me to maintain at the time. I stopped a week early because even I boiled the tap water, the residual chlorine left over wasn't properly broken down by my body (food helps with that normally) and caused strong reactions every time I tried to drink (nausea even vomiting in final week). So not being able to hydrate myself I needed to stop very abruptly.
After I reintroduced my body to food I ended up in hospital a week later due to kidney stones (presumably a side effect of the starvation diet and flushing them out)
The hunger goes away after the 3rd/4th day and I was even able to go for a small run every other day until week 5. My motivation for it was neither religious nor to loose weight (although I had 10kg too much compared to my ideal shape 5 years before). People thought I was crazy for doing it (and I didn't tell anyone about it while it happened and also refused to discuss it with my doctor). I wanted to see how my body (and mind) reacts to extreme pressure like that. Also I felt experienced enough at the time to do this I would not recommend pushing too far into the extreme especially if it's your first time. Also worth noting that my weight never bounced back and I managed to maintain my ideal even after 5 years later (only gained 5kg mostly bodymass I lost not so much the fat).
My mental abilities (creativity, concentration, focus) were incredible especially until week 5. What I learned is as the body prepares for starvation it also releases huge amounts of energy that is stored up. Feels like having super powers. The body makes these reserves available so we can give it a final push for hunting or finding food (when homo sapiens is out in nature trying to survive I guess). It's probably why fasting is such a big thing in every religion.