As those before me have said, increase your water intake. I almost always carry a bottle of water with me along with my vaporizor wherever I go.
Coffee & tea can dehydrate you because of their caffeine content. Juice is fine, and you'll get vitamin C along with the hydration.
Propolyne glycol (pg) and vegetable glycerin (vg) both are humectants, meaning that they naturally attract water to them from the mucous membranes. Hense the dry mouth, throat, and nose when vaping.
If it continues to be a problem for you despite upping your water intake, some people claim that Biotine helps.