Some of the symptoms are: dizziness, headache, inability to urinate, dry mouth and nose, uneasiness etc.

Dry mouth

The signs and symptoms of dehydration range from minor to severe and include:

Increased thirst
Dry mouth and swollen tongue
Weakness
Dizziness
Palpitations (feeling that the heart is jumping or pounding)
Confusion
Sluggishness fainting
Fainting ...more

Mild symptoms of dehydration are characterized at first by increased thirst, and can progress to a more serious condition if the need for liquid is not met. Some of the other symptoms of mild dehydration, along with being thirsty, would be a drying out of the skin, a loss of appetite, the skin will appear flushed, urine becomes dark colored, the mouth will be dry and sticky, fatigue and weakness will occur, you may have the 'chills', and a feeling of being lightheaded upon standing.