How Much Water Should You Drink Per Day? — Science-Based Guide

The 8-Glasses Myth

You have probably heard the advice: drink 8 glasses of water per day. But where does this number come from, and is it actually correct?

The 8x8 rule (eight 8-ounce glasses, totalling about 2 litres) has no strong scientific origin. It likely stems from a 1945 US Food and Nutrition Board recommendation that was taken out of context. The original statement noted that most of this water would come from food.

What Science Actually Says

The National Academies of Sciences, Engineering, and Medicine determined that adequate daily fluid intake is approximately:

• Men: About 3.7 litres (125 oz) of total water per day
• Women: About 2.7 litres (91 oz) of total water per day

This includes all fluids and water from food, which typically accounts for about 20% of total intake. So the actual drinking water recommendation is:

• Men: About 3 litres (13 cups) of beverages per day
• Women: About 2.2 litres (9 cups) of beverages per day

Factors That Increase Your Water Needs

Exercise

Any activity that makes you sweat requires additional water. Drink 500ml before exercise, 200ml every 15-20 minutes during, and replace 150% of fluid lost after.

Hot Weather

Heat increases sweat production. In temperatures above 30C, add 500-1000ml to your daily intake.

Altitude

At elevations above 2500m, you lose water faster through increased respiration. Add 500ml per day.

Pregnancy and Breastfeeding

Pregnant women need about 2.5-3 litres per day. Breastfeeding mothers need 3-3.5 litres to support milk production.

Illness

Fever, vomiting, and diarrhea cause rapid fluid loss. Increase water intake and consider oral rehydration solutions.

How to Calculate Your Ideal Intake

A simple formula based on body weight:

1. Take your weight in kilograms

2. Multiply by 30-35ml

3. Add 500ml for every 30 minutes of exercise

Example: A 70kg person who exercises for 30 minutes daily: 70 x 33 = 2,310ml + 500ml = 2,810ml per day.

Signs You Are Dehydrated

• Dark yellow urine (should be pale yellow)
• Headaches that improve after drinking water
• Fatigue and difficulty concentrating
• Dry mouth, lips, and skin
• Dizziness when standing up
• Reduced urine output (fewer than 4 bathroom visits per day)

Signs You Are Drinking Too Much

Yes, overhydration is possible (hyponatremia):

• Nausea after drinking water
• Headaches despite drinking plenty
• Clear, colourless urine consistently
• Confusion or disorientation
• Swollen hands and feet

Tips for Drinking More Water

1. Start your day with water — drink 250-500ml immediately upon waking

2. Eat water-rich foods — watermelon, cucumber, oranges, and soup

3. Set reminders — use an app like WaterPing to track intake

4. Carry a water bottle — having water visible and accessible is half the battle

5. Flavour your water — add lemon, cucumber, mint, or berries

6. Drink before meals — a glass of water 30 minutes before eating aids digestion

The Bottom Line

There is no magic number. Your ideal water intake depends on your body weight, activity level, climate, and health conditions. Use the formula above as a starting point, monitor your urine colour, and adjust accordingly.

The best hydration strategy is one you actually follow consistently. Tools like WaterPing make it easy to track your intake and build lasting hydration habits.