How Much Water Should You Actually Drink Per Day?
The real answer to daily water intake — not the '8 glasses a day' myth, but what the science actually says.
3 min read · Updated 2026-04-01
For informational purposes only. This content is not a substitute for professional medical advice. Always consult a qualified healthcare provider before making health decisions.
"Drink 8 glasses of water a day" is one of the most repeated pieces of health advice — and one of the least supported by evidence. Here's what actually determines how much you need.
The Real Recommendation
The National Academies of Sciences recommends:
- Men: about 3.7 litres (125 oz) of total water per day
- Women: about 2.7 litres (91 oz) of total water per day
But this includes water from all sources — not just drinks. About 20% of daily water intake comes from food (fruit, vegetables, soup, and even bread contain water). So actual fluid intake targets are:
- Men: approximately 3 litres (about 13 cups) of beverages
- Women: approximately 2.2 litres (about 9 cups) of beverages
These are averages for sedentary adults in temperate climates. Your actual needs vary significantly.
What Affects How Much You Need
Exercise: you can lose 1–2 litres per hour of exercise through sweat. Drink before, during, and after.
Climate and heat: hot or humid weather increases sweat and fluid needs substantially.
Body size: larger bodies need more water than smaller ones.
Diet: a diet high in fruit and vegetables provides more water; a diet high in salty or processed food increases needs.
Pregnancy and breastfeeding: significantly increase fluid requirements.
Illness: fever, diarrhoea, and vomiting cause rapid fluid loss that needs to be replaced.
The Easiest Way to Know If You're Drinking Enough
Check your urine colour.
- Pale yellow (like lemonade): well hydrated
- Clear: possibly over-hydrated (rare, but not necessary)
- Dark yellow or amber: mildly dehydrated — drink more
- Dark orange or brown: severely dehydrated — drink significantly more
This is more reliable than tracking cups because your needs change daily based on activity, weather, and food intake.
Do Coffee and Tea Count?
Yes. Despite the myth that caffeine is dehydrating, research shows that moderate coffee and tea consumption contributes to daily fluid intake. The diuretic effect of caffeine is mild and doesn't offset the fluid consumed.
Alcohol, however, is genuinely dehydrating — it suppresses the hormone that helps your kidneys retain water.
Signs of Dehydration
Mild dehydration (1–2% of body weight in fluid lost):
- Thirst
- Dry mouth
- Darker urine
- Fatigue
- Mild headache
Moderate to severe dehydration:
- Dizziness
- Rapid heartbeat
- Confusion
- Very dark or no urine for 8+ hours
Thirst is actually a reasonably good indicator — if you're thirsty, drink. But don't wait until you're thirsty to drink at all; by the time you feel thirst, mild dehydration has already set in.
A Practical Approach
- Start the day with a glass of water before coffee
- Drink a glass with each meal
- Carry a water bottle and sip throughout the day
- Drink more on hot days or when exercising
- Use urine colour as your feedback mechanism
You don't need to obsessively track ounces. Keep a water bottle accessible, drink when thirsty, and check your urine colour occasionally.