What is the earliest sign of dehydration?

• A. Headache
• B. Muscle Cramps
• C. Dark Urine
• D. Significantly Reduced Work Capacity

Answer: (C)

The earliest sign of dehydration is dark urine. When the body loses fluids, the kidneys work to conserve water, which concentrates the urine and makes it look darker. This change in urine color can appear before other symptoms become obvious, so it’s a practical and quick flag that hydration is slipping.

In firefighter rehab, monitoring urine color is a useful, immediate check during and after exertion in hot environments. Aim for pale straw-colored urine as a sign of good hydration; darker urine suggests you should increase fluid intake. Other signs like headaches, muscle cramps, or a sharp drop in work capacity tend to show up later as dehydration becomes more significant or as electrolyte balance is disturbed.