Which of the following is a common symptom of dehydration?

Dry mouth is indeed a common symptom of dehydration. When the body is low on fluids, the salivary glands produce less saliva, leading to a feeling of dryness in the mouth. This is the body's way of indicating that it needs more water to restore hydration levels.

In contrast, frequent urination usually indicates adequate hydration levels, as the kidneys effectively filter excess fluids. Swollen feet may be associated with a variety of conditions, but is not typically linked to dehydration. Increased thirst is another common symptom of dehydration, signaling to the individual that they need to drink more fluids, but it is not the only indicator of dehydration, whereas a dry mouth is a direct physical symptom.