\~1L per day if sedentary, sipping it (big sips for me at least) gets me by. If I walk a few miles or stand a lot, it ends up being closer to 2L.
It’s normal to get the shits even if you’re not drinking the stuff – your body’s metabolism is making big changes and a lot of water has to leave by whatever exit it can find lol.
But remember if you’re still drinking coffee its a diuretic etc. tons of stuff can give you diarrhea not just snake juice. If its your first multi-day fast just expect watery stools. As long as you stay consistent and keep the refeeds sensible (keto-ish) your body will get used to it and you won’t poop anything for days and days!