There are a number of causes of dry mouth. Some medications, especially antihistamines, can make you feel dry. Hot weather, salty foods and exercise are common culprits, as well. The easy answer is to drink water, and plenty of it. The average adult needs about eight glasses of water a day, more if you sweat a lot.
Water really is the best answer to thirst.
If you're sure you're getting enough water but your mouth is still dry, doctors at UT Southwestern Medical Center at Dallas suggest rinsing your mouth with water. Instead of just gulping the water down, swish it around in your mouth. You can also try rinsing your mouth out regularly with an invigorating mouth wash, but be sure to spit it out instead of swallowing. Other ways to keep your mouth feeling moist include sucking on mints or lemon candy, chewing sugar-free gum, or letting ice cubes slowly melt in your mouth. If you find yourself abnormally thirsty for a long period of time, you're drinking plenty of water and aren't taking any medication that causes dry mouth, talk to your doctor.