The point of the snake juice is to keep your electrolytes up so you aren’t crashing while fasting. If you drink fresh water you’ll just dilute and flush the electrolytes in your system so I would avoid it altogether while fasting.
As for how much snake juice, Cole recommends 1.5 to 2 liters a day. When I first started I was drinking maybe 3 liters a day but I’ve noticed the amount I’m drinking has gone down and yesterday I drank less than 2. As long as you’re drinking snake juice, you’re good, though I wouldn’t recommend chugging it all day as it’s a pretty effective laxative lol. Just make up a couple liters and sip it throughout the day.