Hydration is the level of water within the body. Insufficient hydration causes a dry surface of the vocal folds, as well as less effective movement and repair within the cells of the vocal folds. This impairs the vocal folds' ability to voice efficiently. Adults need two to three liters of liquid intake a day (including liquid in food). Children require one to two liters. The best way to monitor your level of hydration is to make sure your urine is pale.