It already stops being healthy past 3 liters. Your urinary tract is constantly running on overdrive and you are flushing important nutrients out of your system drinking this much.
Plus, you probably can’t get a full night of sleep because you have to take a piss every 20 minutes
Urine isn't the only way to get rid of water. But if you sweat it out, you will need to replace the missing sodium. Breathing causes water to leave too.
Timing is everything. Your kidneys can potentially make a liter of urine an hour. If you drink nine in two hours, you're going to have diarrhea, vomiting and potentially die. If you do the same over 24 hours and you're otherwise healthy, you'll just pee a lot.