Dehydration Symptoms in Adults: Signs, Urine Colour Chart and What to Drink

"Dehydration symptoms" is one of the most searched health phrases in India every summer, and for good reason. Mild dehydration is easy to miss, and it affects how you feel and think well before you feel thirsty enough to notice. Here's how to recognise it at each stage, how to check yourself in ten seconds, and what to drink.

What dehydration actually is

Dehydration means your body has lost more water than it has taken in. Physiologists measure it as a percentage of body weight: a 70 kg adult who loses 1.4 kg of fluid is 2% dehydrated.¹ In India the usual causes are sweat (heat, exercise, outdoor work), not drinking enough on busy days, and illness: diarrhoea, vomiting and fever.

Dehydration symptoms in adults, by severity

Mild (about 1–2% of body weight)

• Thirst and a dry mouth
• Darker yellow urine
• Headache
• Tiredness, low mood, finding it harder to concentrate

The mood effects are well documented. In controlled trials, young women at about 1.4% dehydration reported worse mood, more headaches and lower concentration,² and young men at about 1.6% made more errors on vigilance tasks and felt more tense and fatigued.³ That's roughly the deficit you can build up on a hot commute and a busy morning.

Moderate

• Peeing less often
• Dizziness or light-headedness when you stand up
• A racing heartbeat
• Feeling unusually weak

Severe: a medical emergency

• Confusion, drowsiness or irritability
• Little or no urine for eight hours or more
• Fainting, a fast weak pulse or rapid breathing
• Sunken eyes

Severe dehydration needs medical care, often intravenous fluids. Call 108 or 112, or get to a hospital. Children and older adults dehydrate faster and show it less clearly.

The urine colour check

The simplest home test is the colour of your urine. Researchers validated an eight-shade scale against lab measures (urine specific gravity and osmolality) and found it accurate enough for field use, though not for the lab.⁴ Pale straw is good. Dark yellow or amber means drink. Brown or red needs a doctor, not a glass of water.

One catch: B-vitamins, especially riboflavin (B2), turn urine bright yellow for a few hours. If you take a multivitamin or an electrolyte drink with B-vitamins, that colour doesn't mean you're dehydrated.

Common causes in India

• Heat and humidity. Humid air slows sweat evaporation, so you sweat more for the same cooling.
• Exercise, especially outdoors and in summer.
• Air-conditioned offices. AC itself doesn't dehydrate you much, but dry air and long meetings mean people simply drink less.
• Diarrhoea, vomiting and fever, which lose water and sodium fast.
• Alcohol, which increases urine output.

What to drink when you're dehydrated

Mild, from everyday life: water is fine. Drink steadily rather than gulping a litre at once. Tea, coffee, milk, buttermilk and fruit all count.⁵

After heavy sweating: add sodium. Drinks with electrolytes are retained better than water. In one trial, ORS and milk both kept significantly more fluid in the body over four hours than still water.⁶ An electrolyte drink like Flow or a salty snack with water works.

From diarrhoea or vomiting: use WHO-formula ORS, in small frequent sips.⁷ See ORS vs electrolyte drinks.

Don't overcorrect. Forcing down litres of plain water can dilute blood sodium, a condition called hyponatremia, especially during long events.⁸

How to prevent it

• Keep water in sight: on your desk, in the car, in your bag.
• Drink with every meal. ICMR's guideline is about 2 litres of fluid a day for a healthy adult, more in heat or with exercise.⁹ More on that in how much water you need a day.
• Check urine colour mid-morning and mid-afternoon.
• On hot days, plan sodium as well as water. See our heat stroke guide.