It's dehydration!Even if you're just a little short of water, your vocal cords will suffer to some degree or another, because your body doesn't consider them as first priority for scarce h2o. You can read my article about hydration and the voice at the H2O Overdrive site.
So what do you do if you are in need of a quick fix (you don't have time to let your body absorb in the usual time-lag way the water you drink that your voice needs)? I have three suggestions:
1. Drink a diluted solution of 25% pineapple juice (a little can of Dole's will do) and 75% water. The pineapple juice has enzymes that make the throat feel wonderful.
2. Drink one of the products they sell at the H2O Overdrive site. These formulations really are fantastic. I like diluting mine with water, about half and half. I keep them on hand for my own performances.
3. Hydrate yourself through steam before your performance (shower, hot bath, warm air humidifier).
But the best thing of all to do is stay hydrated on a regular basis. A good rule of thumb I've heard from nutritionists is to take your weight, divide in half, that's the average ounces of water you should drink daily.
Think this fix is too simple to be that important?
Let me answer with old proverb... possibly dating in some form back to the first century:
"For The Want Of A Nail"
For want of a nail the shoe was lost.My paraphrase would end with the line:
For want of a shoe the horse was lost.
For want of a horse the rider was lost.
For want of a rider the message was lost.
For want of a message the battle was lost.
For want of a battle the kingdom was lost.
And all for the want of a horseshoe nail.
"For the want of water the voice was lost." Word to the wise:)