Here goes nothing.
So, I would hope you’re not new to water fasting with a goal like that. And if you are, you should really reconsider. That’s probably pushing the limits too far, but hey if you’ve gone more than a month before then it’s not my call. If this doesn’t apply, then good luck!
That sounds quite extreme. It may be much easier for your physically and mentally if you break it up like five 20 day fasts or four 25 day fasts or something like that. And eat keto in between so you stay in ketosis. That should go much easier. If you are set on doing 100 days straight, do not do it without medical supervision!