On a daily basis, most people get enough fluid through normal drinking behavior, such as drinking with meals and snacks. However, thirst isn’t always a reliable gauge of hydration status, especially in children and older adults. A better barometer is the color of the urine. For most healthy individuals, clear or light-colored urine suggests adequate hydration, whereas a dark yellow or amber color usually signals dehydration, although certain medicines and vitamins may cause the color of the urine to change, making this test unreliable. Infrequent urination and low urine volume can also suggest inadequate hydration.
Mild dehydration can affect physical and mental performance and contribute to unpleasant physical symptoms like headaches and muscle cramps. The early signs of dehydration can be non-specific, usually involving fatigue, headache and confusion. Oral rehydration is usually all that is required. But because severe dehydration can be life-threatening, medical help should be sought quickly if there is any concern about someone needing more aggressive fluid supplementation. However, severe dehydration can be life-threatening.
Because dehydration can develop quickly under some conditions, it’s important to recognize the following signs of dehydration in others and act quickly to help them cool down and rehydrate.

Signs of Dehydration

  • Increased thirst
  • Dry or sticky mouth
  • Light-headedness or headache
  • Fatigue
  • Impaired mental focus
  • Low urine output
  • Inability to produce tears
  • Dry skin
References:
Urinary indices of hydration status. Armstrong, L.E., Maresh, C.M., Castellani, J.W., Bereron, M.F., Kenefick, R.W., LaGassee, K.E., and Riebe D. Int J Sport Nutr. 1994 Sep;4(3):265-79.