I agree with what everyone else is saying that you should contact your medical professional and ensure there’s nothing amiss.
However this also happened to me. Extremely dry lips, mouth, and no matter how much water I still felt so thirsty. For me it was electrolytes and I was unintentionally going into keto. I started taking a keto electrolyte supplement every morning. No problems since.
Intense dry mouth is not clinically associated with hyponatremia. There are other known causes of chronic dry mouth, which a doctor can help identify.
My suggestion is to do as the others here have suggested - talk to your medical professional. At the same time, examine which changes in behavior or consumption have accompanied your new symptoms. If it’s only your water consumption, ease off and see if it helps. If there’s anything else, take a look at that.
But see a doctor. There’s no substitute for this advice.
Also add magnesium and potassium for complete electrolytes. As for the dehydration, I had the same issue every time I upped my water intake, never outside of it. Nurse practitioner told me that when you increase your water intake, the water you drink will “stick to” water currently in your body so when you pee, you’re peeing out more than what you drink, causing the dehydration. This will go away when your body acclimates to the intake. Everyone saying it’s diabetes isn’t considering the fact that this only started when you increased your water intake.