Which of the following is NOT a sign of dehydration in an adult?

Excessive sweating is not typically considered a sign of dehydration in an adult. In fact, sweating is a mechanism through which the body regulates temperature and can help maintain fluid levels under normal circumstances. When people sweat, they are usually losing water, which would indicate a need for rehydration rather than dehydration itself.

On the other hand, thirst is a well-known signal from the body indicating the need for more fluids. A dry mouth is another clear indication that the body is experiencing insufficient hydration, as the salivary glands reduce production when dehydrated. Dark urine is often a sign of dehydration as well, since concentrated urine appears darker when there is not enough water in the body to dilute it; it reflects higher levels of waste products due to reduced fluid intake. Therefore, while excessive sweating can occur during physical activities or hot conditions, it does not connote dehydration, making it the correct choice for this question.