We’ve all heard the numbers: drink eight 8-ounce glasses of water a day for optimum hydration. Unfortunately, this is a debunked theory, just like the old food pyramid. In actuality, there’s still science being conducted researching the exact amounts of water a person needs to drink every day and how this contributes to overall health (1), though various guidelines have been developed (2). There’s also more research being conducted regarding the difference between total body water and extracellular water balance, diagnosing the balance between the two, and how they relate to the body’s hydration homeostasis and intercellular water balance, but those concepts seem to come more into play when there’s a pre-existing medical condition (3). However, the “one size fits all” idea has decidedly been nixed. It makes sense, really. A 25-year old NFL linebacker who’s extremely active and sweating a lot on the daily needs to replenish more fluids than an 80-year old petite librarian who’s not doing much throughout the day.
The foods we eat will also contribute to our overall hydration needs, but that only constitutes around 20% on average (1,2). It may seem obvious, but the higher the water content in your food (think fruits and veggies), the higher hydration percentage you get from your diet. We still need to drink fluids to maintain the normal water content in our bodies, which is between 75% water in infants to 55% water in the elderly (1). Something that the science is also trying to validate is the body’s need for actual water instead of sugary fluids, such as pop (yes, POP), fruit juices, or alcoholic beverages. Though the science isn’t conclusive about pure water’s superiority in hydrating the body compared to other drinks, it’s the issue of everything ELSE in them that can contribute to decreased health and wellness (I’m looking at you, sugar and caffeine).
So what’s a good rule of thumb? Again, there are different statistics out there. Some sources say times your body weight by 2/3 and that’s the ounces you should be drinking each day. Other sources say you should be drinking between 0.5-1 ounce per pound that you weigh. You can Google till the cows come home and not find a consistent answer across the board. A fun website with some medical backing is: www.h4hinitiative.com. There’s a feature that allows you to fill in certain statistics about yourself and it tells you your water input needs, taking things like physical activity and age into consideration.
The simplest way of gauging your personal hydration needs? Listen to your body. If you’re thirsty, drink water. This is especially important to pay attention to when you’re actively making a lifestyle change, whether it’s through modifying your food intake, being more physically active, or a combination of the two. Have an idea about what the guidelines are for your age and physical regiment, however, to ensure you’re not falling too short of your general hydration needs (you can take an average of the recommended ounces from the different sources to get this goal number of ounces). You can also monitor your urine; a clear to light yellow color tends to indicate good hydration, while a dark yellow or orange color typically indicates dehydration (4) (keep in mind any supplements or dietary items that might affect this—for example, turmeric/curcumin can turn your urine a vibrant yellow color).
A word of caution: if you’re thirstier than normal to the point where you can’t satiate your thirst, no matter how much water you’re drinking, this could be polydipsia and you should consult your GP about the situation. Because your body regulates its water needs through a combination of organ and hormone systems, any disruption of those systems can have an effect on your overall hydration homeostasis. Serious circumstances could be the cause, such as organ failure, various forms of diabetes, or even sepsis.
Popkin, Barry M., Kristen E. D’Anci, and Irwin H. Rosenberg. “Water, Hydration and Health.” Nutrition reviews. 2010; 68(8):439–458.
Institute of Medicine. 2005. “Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate.” Washington, DC: The National Academies Press. https://doi.org/10.17226/10925.
Roumelioti, Maria-Eleni, et al. “Fluid balance concepts in medicine: Principles and practice.” World J Nephrol. 2018 Jan 6; 7(1):1–28.
Shirreffs, S M. “Markers of Hydration Status.” European Journal of Clinical Nutrition. 2003; 57:S6-S9.