CICO diet along with exercise/workouts or drastically do cardio to lose your muscles if you don't wanna be fit. Once again, it's pointless to look at weight when it's body fats that matter, you can look hench at 80kg but look fat at 70kg.

Even if you can hold your temptation to eat, you still can't lose that much of weight in this short period, lol. Moreover, the weight difference will immediately be reversed after you start eating back, not to mention your body will be having many problems like fatigue, faint, etc, during the water fasting. And one more thing, rapid weight loss may lead to loose(saggy) skin and it's usually something that can be surgically removed only.

Mate, BMI is a pretty inaccurate tool to determine whether you're healthy or not. Like I said many times, BF% and waist circumference are what you should take care of. Aim for <20 BF% and <40" waist circumference if you're male, <35" if you're female, and build some muscles then you're good enough already.