I'm not sure if this would be helpful to you but here goes...
After my Water Fast I kept having this dry throat and thirst that you are describing.
After numerous doctor visits and weeks of suffering, the end results were as follows:
After you experience water fasting, your body cannot tolerate overeating the same way it could before.
Fruit for me is an no-no. The crazy thing is that I can eat Snickers or ice-cream but fruit is off limits because it is an diuretic and it produces that dry throat & thirst. My throat closes up.
Some of the things in our diet we have accumulated a tolerance for. After fasting, it like our body takes the mask off and alerts us to the things we were originally sensitive/allergic to. For me, garlic has an extremely extremely pronounced effect on the dry throat and thirst. My throat now closes up. Before the fast I ate garlic on EVERYTHING. Now I cannot tolerate it period. I said that to say this: It may be something you are eating. Write down everything along with the quantity of each item. Cross check symptoms/food with the FODMAPS lists.
No amount of water I drunk would quench the dry throat and thirstiness. It was like my body was not absorbing water at all! It got so bad that my whole body broke out into these clear air bubbles.
Just a few possibilities. Please let me know what you figure out.