Hey I had this same problem, I accidentally stumbled across the cure ..trying to help my cellulite.. I ate extra lecithin and glucosamine /choindroiton. Although I think it was just the lecithin that cured my insatiable thirst.
I had to urinate frequently and if I did have a bottle of water with me at all times I would literally panic. I was so thirsty it was like having cotton mouth 24/7. It took about 1to 2 months on this regimen. The bonus is if you have cracked heels like i did they get repaired on this program. Good luck.