When it comes to our daily water intake, there’s a lot of information out there stipulating exactly how much we should be drinking. Some say 2L, some say 8 glasses. But who do we listen to? And furthermore, is this intake the same for everyone?
Water is the most underrated, yet arguably the most important ‘nutrient’ for protecting our health. It forms the basis of blood, which flows through all parts of our body, providing nutrients, oxygen and other life essentials. It is also a medium for eliminating metabolic wastes (urine), and transporting digestive enzymes into our gut. In fact, the human body is at least 50-75% water, and our fluid balance tightly controls many bodily functions. A shift of 2% to hydration status can result in dizziness, loss of consciousness, cardiovascular impairments, or even more serious consequences for those with existing health conditions. Long term, mild dehydration can contribute to fatigue and reduced performance. It can also lead to reduced kidney function and renal stones (1). Hydration is so important, that humans can survive for 3 weeks without food, but only a handful of days without water (2)!
Unfortunately, our bodies are not very intuitive when it comes to maintaining hydration. We often mistake thirst for hunger, or only feel the urge to drink when our body water has already dropped at least 1% (2). Because of this, we have come to rely on fluid recommendations, such as ‘aim for 2L a day’ or ‘aim for 8 glasses a day’, in order to benchmark our hydration needs. But do these targets apply to everyone?
According to Professor Tim Crowe, nutrition researcher and expert from Deakin University, it is a myth that everyone needs to drink 8 glasses, or 2L of water a day. He explains that there is no scientific evidence to back this recommendation. The Australian Dietary Guidelines confirm this, stating ‘there is no single level of water intake that would ensure adequate hydration and optimal health for the apparently healthy people in the population’ (3).
As a rough estimate, the fluid requirement for healthy adults is 25 – 35mls per kilogram of body weight. For example, a 60kg female’s fluid requirements will be 1.5 – 2.1L per day (4). A good way to check whether you are meeting your fluid requirements is to check the colour of your urine - it should be pale yellow.
However, Crowe explains that we don’t need to meet our fluid requirements entirely by drinking water (3). In fact, up to 30% of our fluid requirements can be met with a healthy diet, including foods with a high water content. Even tea and coffee can contribute - their mild diuretic effect is insignificant compared to the greater volume of fluid retained after drinking. Unfortunately, alcohol is the only fluid that is dehydrating (go figure!)
To create a hydration plan that works for you, first use the above equation to calculate your fluid requirements. Then, see how you can reach your personal targets using a combination of fluids and hydrating foods. A handy hint, if you meet 70% of your calculated fluid requirements with water, and consume the recommended five servings of vegetables and two servings of fruit per day – you’re all set.
Fish and seafood 80%
Meat and poultry 75%
Boiled rice and grains 67%
Soup >90%, depending on ingredients chosen
Juice 80-90%, depending on ingredients chosen