Hepatologist says ‘8 glasses of water a day’ is a myth: Here’s how much you should drink to stay hydrated

Hepatologist Dr. Abby Philips debunks the “8 glasses a day” water myth and shares expert tips on how much you really need to stay properly hydrated.

For decades, the recommendation to drink eight glasses of water a day has been ingrained in our minds as a golden rule for good health. However, Dr. Cyriac Abby Philips, a certified hepatologist popularly known as The Liver Doc, says this advice is more myth than medicine. In his May 8 Instagram post, he explains why the "8 glasses a day" rule doesn't hold up and what you really need to know about staying properly hydrated.

"I cannot believe I'm making a post for adults about how and when to drink water in 2025. But I guess this is important because people have lost critical thinking skills and keep asking me this question in the messages. So here goes," Dr Abby wrote in the caption. Let's take a closer look at what he recommends:

What does our body actually lose? Understanding fluid loss

Our bodies lose water constantly, even when we're resting. Here's Dr Abby's breakdown of daily fluid loss for a healthy adult in a comfortable environment (20-25°C):

• Urine: About 500 mL per day, which helps clear metabolic waste if the kidneys are working efficiently.
• Stool water: Around 100 mL per day.
• "Insensible" losses: Approximately 700 mL daily through breathing and passive evaporation from the skin.

Put together, that's roughly 1.3 to 1.5 litres of water lost every day, even if you're sedentary and in mild weather.

How much water should you consume

To avoid dehydration, you need to replace at least what you lose daily. For a healthy adult at rest:

• The practical minimum fluid intake (including drinks and water contained in food) is about 1.5 litres per day.
• About 20% of this water comes from the moisture in your food. This amount varies by diet, fruits and vegetables have high water content, meats have moderate and processed or baked goods have low water content.

Factors that change your fluid needs

• Activity and heat: Sweating can cause you to lose anywhere from 0.3 to over 2 litres per hour. The American College of Sports Medicine recommends adding 0.4 to 0.8 litres of fluid for every hour of vigorous exercise to prevent excessive body mass loss.
• Children: Fluid needs vary by age and activity level, about 1.3 litres per day for ages 2-3 and 1.6 litres for ages 4-8.
• Pregnancy and lactation: Pregnant women need an extra 300 mL per day in the later trimesters, and breastfeeding mothers require about 700 mL more daily.
• Older adults: Although they still need 2-3 litres per day, their thirst perception and kidney function decline, so they must be conscious about drinking enough.

How much is too much?

Healthy kidneys can clear about 0.8 to 1 litre of dilute urine per hour, up to roughly 24 litres a day. Drinking more than 1 litre per hour for several hours can overwhelm this capacity, diluting blood sodium and risking a dangerous condition called hyponatremia, which can cause brain swelling and seizures.

What's a practical hydration plan?

• Basic plan: About 1.5 liters per day of total fluids (water plus other drinks and food moisture) is enough for a resting adult in mild weather.
• Advanced plan: For most healthy adults, 2 to 4 litres per day covers ordinary living conditions, while 6 to 7 litres per day can support heavy training or intense activity.
• Only in extreme cases, like endurance events or desert conditions, would fluid needs exceed 10 litres per day, and only under medical supervision.

How to stay hydrated without overdoing it

• Forget the "eight glasses" myth.
• Instead, pay attention to your body's signals:

-Your urine should be clear or pale yellow.

-Your body weight should remain stable.

- You should be able to remember the last time you felt genuinely thirsty.

• If you're dealing with higher fluid loss situations, heat, long flights, breastfeeding, certain medications, or exercise, you'll need to drink more, but more is not always better because your kidneys regulate how quickly your body can process fluids.

Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. Always seek the advice of your doctor with any questions about a medical condition.