A few weeks ago, my mother-in-law saw me chug water from my 64-ounce Hydro Flask – it was impressive, I drank several cups of water in a gulp. She looked stunned and asked me how much water I drink a day. I had no clue; my water intake has been based on how I am feeling. At no time, have I ever kept track of how much water I consume in a day. So, over the last several weeks, I tracked my water intake. On average, I drink about 200 ounces of water a day – and up to 220 ounces on the days I workout. That is equivalent to 6 to 7 liters or 25 to 28 cups a day. This was a bit of a surprise. I started to wonder, is there a right amount of water you should drink per day?
In my search for answers, I tried numerous online water intake calculators. The results recommended I drink from 1.9 liters to 3.7 liters a day. I was not satisfied with the results because the answers varied widely – not surprising because each calculator used completely different sets of data points to reach a conclusion. Maybe the calculators can provide a decent baseline, but there is no way I will feel physically okay drinking only 2 to 3.7 liters a day. When I don’t drink enough water, my body immediately lets me know I am getting dehydrated. I get terrible dry mouth, a headache, and bright yellow urine.
Daily Water Intake Recommendations
The commonly cited recommendation is to drink eight 8-ounce glasses of water a day, which is about 2 liters, or half a gallon. The recommendation to drink eight glasses of water a day, also known as the “8×8 rule,” is often attributed to a guideline from a 1945 report from the Food and Nutrition Board of the National Research Council – which recommended that adults drink 1 milliliter of water for every calorie consumed—or around 2 liters for a 2,000-calorie diet. However, it’s worth noting that this guideline was not based on scientific evidence but rather a general recommendation for total daily fluid intake, including water, beverages, and food. So, this is a general guideline and may vary depending on individual factors such as age, weight, sex, activity level, and climate.
Both the Cleveland Clinic and Mayo Clinic cite a 2004 article from the National Academies of Sciences, Engineering, and Medicine (National Academies of Sciences, Engineering, and Medicine. (2004). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: The National Academies Press. doi: 10.17226/10925.) that determined the adequate daily fluid intake is:
- About 3.7 liters (125 ounces or almost 16 cups) for men, and
- 2.7 liters (91 ounces or almost 11.5) for women.
This includes all beverages and water from food.
Again, I think these recommendations will serve as a decent baseline, but there are too many individual factors that are not accounted for in these recommendations. I suspect this is why it is difficult to find a general scientific consensus on water intake.
No One-Size-Fits-All For Hydration, But We All Have A Thirst For It
The idea that there is a specific, universally recommended daily water intake is a bit more nuanced than a simple yes or no. This 2002 article, Variation in Human Water Turnover Associated With Environmental and Lifestyle Factors, finds that some people may not even need eight 8-ounce cups of water per day. The authors explain “that one size does not fit all for drinking water guidelines, and the common suggestion that we should drink eight 8-ounce glasses of water per day (~2 liters) is not backed up by objective evidence.” I can hear the water bottle lobbyists losing their mind right now.
First, you need to listen to your body. Your body knows how to regulate itself. When the body needs more water, such as during times of increased physical activity or in hot weather, the brain signals thirst to encourage you to drink more fluids. Additionally, the kidneys play a crucial role in maintaining the body’s water balance. They adjust the amount of water excreted in urine based on the body’s needs, helping to retain water when you need it and excrete excess water when you have consumed more than you need.
Second, while scientific recommendations possibly provide a helpful baseline for daily water intake, it’s important to recognize that individual hydration needs can vary widely. Factors such as age, weight, activity level, climate, and overall health can all influence how much water your body requires.
Therefore, while the general guideline of 8 glasses a day may be a decent guideline for some people, it’s crucial to listen to your body’s signals. Thirst is a natural indicator that your body needs more water, so drinking when you’re thirsty is a simple and effective way to ensure you’re staying properly hydrated. Paying attention to your body’s cues and adjusting your water intake accordingly is key to maintaining optimal hydration levels.