Dx: diabetes inspidus, dry mouth/lips for the last 5 weeks. drinking tons of water. no other signs of dehydration. how to combat the dry mouth/lips?

Multi-strategize!: You are wise to go after the dry mouth; this causes gum disease, tooth decay and a handful of other oral problems. No one answer will address your needs. Water is a start, find a good lip balm that you like; check out biotene saliva substitutes and similar products; evaluate your diet, supplements & medications for other causative factors that could be changed; stay ahead of the oral health game.

Underlying cause: Treat the underlying cause of the di. If this is central di, DDAVP (desmopressin) can help. Otherwise the free water will flow right out of your body.