I am no expert, but done a few fasts. Every time you fast something different happens. I have been fasting for last 2.5 days. I do not feel thirsty at all. Other fasts so far I had to drink water almost every 2 hours.
This time I had one glass in one day, my mouth is watery and I urinate a lot. I would drink by thirst. In my experience, yellow and brown urine means you are detoxing.