Ok, you started the fast that is great. Please make decisions by listening to your body. I think Glittergalaze already told you that. Drinking too much water taxes your kidneys, so drink as per thirst. If your mouth does get dry then drink water.
Dry fast means to not drink water for a day or two. Some people go for a week. I did this in my last fast. During your fast if you are drinking water for a few days you can stop drinking water for a few days. I found that the weight loss was fast and so was detox.
You also do not need laxatives if you have fasted and eat plant based foods or do the MC.