Are you by chance taking any herbs? Some herbs have diuretic properties that are more pronounced when you actually have some water to spare. I've been drinking between 64-96 oz of water a day for a few months, and while doing a Bowel Cleanse with a commercial product I began to have intense dry mouth. In examining the ingredients list I found that it contained dandelion root and cleavers, both very potent diuretics. I upped my water, and kept my salt intake low, and the dry mouth went away. Even if you have been taking a diuretic herb for some time without issue, adding water will make that herb do what it is meant to do, pull water out of the body. If you are not sure if an herb you are taking is a diuretic, google it online, and an information site should tell you some of its properties. Be sure to also check your multivitamins, as they too can contain diuretic herbs.