Persistent dryness of the mouth and tongue despite drinking water can occur due to dehydration, mouth breathing, anxiety, diabetes, vitamin deficiencies, side effects of medicines, infections, or reduced saliva production. Sometimes stress and poor sleep can also worsen dryness. Since the symptom has lasted for days, it is important to check blood sugar levels and review any medicines you may be taking. Sipping water frequently, avoiding caffeine and smoking, maintaining oral hygiene, and using sugar-free chewing gum may help stimulate saliva. Treatment depends on the cause, so medicines should only be taken after proper evaluation. If you also have a fever, mouth ulcers, difficulty swallowing, or weight loss, consult a doctor promptly for further examination.