Is water fasting without doctors consent harmful? Whatare some effects that could occur?

Worst experience ever, I got sick, then got sicker

And ended up in the emergencies.

Yes. You'd be better taking a more modest and sustained approach. It's probably a bad Idea to cut down to less than 500kcals per day for more than a couple of days. A change of lifestyle is preferable to a binge dieting

I fast everyday. I love leangains (16 hour fast 8 hour eating window). My mother was interested as the health benefits are amazing and she started off at 12 hours and increased to 16 hours. We never go hungry (fasting decreases appetite). Check the link below for the different types of fasting and health benefits.

Intermittent Fasting 101 — The Ultimate Beginner's Guide:

https://www.healthline.com/nutrition/intermittent-...

you need bone broths or some other wet nutrients...you need to do better research before you fast...on just water you wont last 3 weeks....

damage to liver and kidneys they require flushing out of toxins regularly

Water diets are a terrible idea.

No calories in = difficulty burning fat.

Since muscle and lean tissue are more easily convertible to energy, then you will lose most of that and keep the majority of your fat, which is exactly the opposite of what you want to achieve.

Muscle and lean tissue weigh more than fat, so it will seem as if you're succeeding, but you will become weak, listless and function poorly.

You're far better off eating smaller portions of quality food and do a minimal amount of exercise.

This will help you burn fat and keep the lean tissue / muscle.

You will then become stronger, fitter, think more clearly, be more productive, healthier, more motivated and feel much better throughout the day.

Btw, any decent doctor wouldn't consent to a water diet, because it's known to be very harmful and sometimes even life threatening.