Water: How Much Is Really Enough?

By Phoebe Chi, MD

So how much water DO you need? Is “8 glasses a day” really true? What if you just don’t like water? Today, I will address the most commonly asked questions about fluid intake and give you essential tips on how much to drink, what to choose, and when.

So how much is enough?

While obviously this depends on many factors–activity level, body mass, the kind of climate you live in, your overall health–the Institute of Medicine has determined that the adequate daily fluid intake for an average person* living in a temperate climate is:

2.2 liters  =  75 oz  =  9 glasses

3 liters  =  100 oz  =  12.5 glasses

But what about for you? If you want to be more precise, you can simply halve your weight (in pounds) to find the number of ounces you should be aiming for each day:

Your weight (lbs) ÷ 2 = Daily goal (oz)

What counts as “fluids?”
  • In short: Everything besides alcohol. Milk and sports drinks are the best alternatives. Juices and broths are also okay, but be mindful of the calorie/sodium content.
  • Caffeinated beverages: People often wonder if  beverages such as sodas, tea, and coffee “count” toward this daily quota. The answer is technically YES. This was initially debated given that caffeine can act as a mild diuretic, but recent studies show that this effect is negligible for most people who drink moderate amounts of caffeine and that it does not offset its hydrating properties. With that said, I personally still try to drink water and coffee in a 1:1 ratio (as it makes me feel more hydrated), and recommend choosing water or lightly flavored water as the healthiest choice for meeting your daily goal.
  • Alcohol: Alcohol does NOT count, and taken alone, it will dehydrate you. Always try to drink water in a 1:1 ratio to any alcoholic beverage.

How to tell if you are getting enough and some tips to help:
  • Check your urine. It should appear nearly clear to light yellow. Darker than that? You are dehydrated and need to start drinking more.
  • Watch for these symptoms: Sometimes the first symptom of dehydration is just fatigue, a headache, or the feeling of not being quite right. So for example, if you are a busy professional who finds him or herself getting frequent headaches and a mid-day slump, it could be dehydration. Try increasing your water intake.
  • Get in the habit of drinking a glass at set times each day: I recommend drinking a glass of water in the morning and before each meal. This is not only a good way to ensure you stay hydrated throughout the day but will also help prevent overeating.
  • And sip throughout the day: Do not wait until you are thirsty to drink. By then your body is already edging toward dehydration. Invest in a nice reusable water bottle and keep it with you during the day.

When should you increase your fluid intake?
  • Whenever you are sick: Changes in metabolic demand during illness increase your body’s fluid requirements. In addition, fever, vomiting, and diarrhea can all quickly dehydrate you. In these cases, sports drinks or oral rehydration solutions such as Ceralyte can offer further benefit by replenishing your electrolytes (see below).
  • Whenever you are at high altitudes: At elevations greater than 8,200 feet (2,500 meters), your physiology changes and your body requires more fluids to function properly. It is recommended that you try to double your fluid intake whenever traveling to these areas.
  • If you are pregnant or breastfeeding: The Institute of Medicine recommends increasing fluid intake to 10 glasses (2.3 liters) when pregnant and 13 glasses (3.1 liters) of fluids when breast-feeding.
  • Whenever you sweat or increase your physical activity in general.

When should you choose electrolyte-containing drinks (eg. Gatorade) over plain water?
  • In short:
    • Whenever you find yourself sweating profusely (for any reason) for more than 1½ hours.
    • Whenever you are sick and are having episodes of vomiting or diarrhea.
  • This is mainly to replace the sodium, potassium, and chloride lost through sweat and body fluids, while adding some nutrients in the form of carbohydrates. So for instance, if you exercise in a cool, dry environment for 2 hours and barely sweat, you would be just fine drinking plain water.

Do you need to worry about drinking too much water?
  • In short: For the average, healthy person: NO. For athletes: Be cautious.
  • In order for a healthy person to get hyponatremia (the serious condition that occurs when you drink so much water that it overwhelms your kidneys and dilutes your body’s sodium), it is estimated that an average person would need to drink approximately 6 liters of water over a very short period of time (such as in a water-drinking contest or in attempt to rehydrate after a marathon). Therefore, for those most at risk (eg. athletes), always drink fluids supplemented with electrolytes when drinking large amounts (eg. after a game).

So with that said, be encouraged to go forth and drink to better health!

*These recommendations do not apply to those with congestive heart failure, renal disease, or certain other conditions. In all cases, do what your trusted health care professional has advised you to do, as the information presented here is only for education purposes only and is not to be taken for medical advice. 🙂

68 thoughts on “Water: How Much Is Really Enough?

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  1. Wow very helpful I don’t even quite near drink 9 glasses of water gotta improve in that thanks for this🙌🏼

    Do check out my blog posts and let me know what you think would love that I’m new to the blogging world 😊

    Liked by 1 person

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