Most of us think drinking water is simple. You’re either thirsty, so you grab a glass, or you’re not, so you skip it. But our kidneys aren’t quite that forgiving. These little organs are busy filtering toxins, balancing electrolytes, and regulating fluids. When you don’t drink enough, they have to work overtime. And that’s not just a mild inconvenience, it can slowly damage their function. Over time, chronic underhydration can increase the risk of kidney stones, urinary tract infections, and even chronic kidney disease.And here’s the kicker: a lot of people think they’re doing enough just because they sip coffee, tea, or juice throughout the day. But beverages with caffeine or sugar aren’t the same as plain water. They can actually pull water out of your system faster, leaving your kidneys scrambling to keep up. Another common myth is that you only need to drink when you’re thirsty. By the time thirst hits, your body is already a little dehydrated. Your kidneys might be silently under strain before you even notice it.Some people go the opposite route and overhydrate, thinking it’s impossible to drink too much. While rare, excessive water can disturb electrolyte balance, which your kidneys have to manage too. The point is, there’s a sweet spot that many of us miss. Your kidneys need consistent, moderate hydration, enough to keep urine pale yellow, not clear like water in a bottle commercial, but not dark either.As per a report, even mild dehydration (1-2% body weight loss) impairs cognition, mood, and physical performance, escalating to kidney injury, UTIs, falls, and delirium in vulnerable groups like the elderly. Chronic low intake links to urolithiasis, constipation, and possibly hypertension via reduced urinary dilution. Hospitalized cases show 15% mortality from complications like sepsis and organ failure; pregnancy raises preterm labor risk.Overhydration or excess fluid (>3-4L rapid intake) dilutes sodium, causing hyponatremia (Na<135 mmol/L), cerebral edema, seizures, or coma, seen in athletes, psychogenic polydipsia, or iatrogenic cases. Human trials (10L/day) induced headaches, confusion, and emotional lability; systematic reviews report 13% mortality in severe oral water intoxication.“Kidneys need the right balance of hydration,” says Dr. Ajay Aggarwal, Consultant – Urology, RG Hospitals. “Everyone preaches “just drink more water” for perfect health, but when it comes to your kidneys, this advice misses the mark big time. These powerhouse organs filter your blood, balance electrolytes, and keep your blood pressure steady but they thrive only on the right fluid levels. Too little or too much can harm your kidneys,” the doctor adds and shares common misconceptions around hydration.

Myth 1: More water always flushes toxins

Gulping gallons to detox might backfire. Over hydration dilutes sodium in your blood, triggering hyponatremia. a condition caused by low levels of sodium, brain swelling, confusion and even seizures in extremes. Your kidneys can’t process endless water fast enough. Moderation rules: aim for clear-to-straw urine, not a flood.

Myth 2: Thirst means you’re fine

Waiting for thirst to strike? You might be too late as by that time mild dehydration already stresses the kidneys by concentrating urine. This breeds stones, crystals, and UTIs. Heat, exercise, coffee, or meds like diuretics up your needs. Monitor your urine color regularly.

The real risks

Chronic under-hydration thickens blood, straining kidney filters, damaging them over time. Overdo it with conditions like diabetes or heart failure? Little known to most, fluid overload can shoot up pressure and worsen failure. Even healthy people risk acute injury from imbalance.

Smart hydration guide

Ditch the rigid “8 glasses” rule. Women should aim for 2.2 liters/day and men for 3 liters, adjusted for sweat and climate. Monitor yourself closely, dark urine indicates more water intake is needed, and clear urine indicates to cut back on it. Kidney patients must seek medical consultation to meet set personalized targets. Drink as much amount of water so that urine output should be at least 1.5 liters/day.Medical experts consultedThis article includes expert inputs shared with TOI Health by:Dr. Ajay Aggarwal, Consultant – Urology, RG HospitalsInputs were used to debunk common myths around dehydration and overhydration.