Why We Need Water

Your body is made up of about 60–65% water, and it can’t produce its own. You lose water constantly through breathing, sweating, and urination — about 1.5 liters per day just from peeing. That’s why drinking enough water is essential. Most adults need 2–3 liters (71–96 oz) of water per day, depending on gender and activity level. Children need less, based on age and size.

Remember the survival rule of 3:

• 3 minutes without air
• 3 days without water
• 3 weeks without food

What Happens When You’re Dehydrated

When water levels drop, your brain goes into action. It releases hormones, slows down water loss, and activates your thirst response. But there’s only one real fix: you need to drink more water. No internal system can replace lost fluids — only you can do that.

Even mild dehydration can cause your brain tissue to temporarily shrink, which affects concentration, memory, and mood. This is why you may feel foggy-headed, irritable, or have trouble focusing when you haven’t had enough water.

Water helps regulate your internal temperature. Without enough of it, your body can struggle to cool down through sweat, putting you at greater risk of heat exhaustion or even heatstroke — especially during physical activity or hot weather.

When you're dehydrated, your blood volume decreases. This forces your heart to pump harder to deliver oxygen and nutrients, which can cause an increased heart rate and lower blood pressure. It’s one reason dehydration can make you feel weak or dizzy.

Your kidneys rely on water to filter waste from your blood. When you're dehydrated, they conserve water by producing less urine — which can become dark and concentrated. Over time, chronic dehydration can increase the risk of kidney stones or infections.

Listen to Your Thirst

Thirst is your built-in alert system. Don’t ignore it. Stay hydrated by drinking clean, fresh water throughout the day. Avoid excess caffeine and alcohol, which can dehydrate you. Taking care of your thirst means taking care of your body.

Learn More About Thirst and Hydration

For more detailed medical information, visit the National Library of Medicine.