There is a striking resemblance between the amount of water on this earth and the amount of water in the human body. With around 60-65% of the human body being water and 75-85% of the brain being made up of water. In this article we are going to look at some of the functions of water, signs and symptoms of dehydration and then try and set some guidelines on how much water might be right for you.
Show me the evidence
Given that we can only last a few days without water, you would think there might be some research looking at the most appropriate levels of water for us humans to drink.
You’ve probably heard of the drink 8 cups (1 cup being 8 ounces/around 250ml) a day recommendation, but the reality is there is very little science behind that recommendation and actually very little science looking at water intake in general.
In fact, the Institute of Medicine following some published reviews of that recommendation found it to largely underestimate fluid needs for most individuals. They stress the importance of individualisation, but then recommended 11-plus 8-ounce cups for women and 15-plus 8-ounce cups for men.
Please note this does not include what we get from food which would be around 20% of this total, so the final number of cups for women would be around 9 and men around 12.5.
Most research on fluid levels/hydration status comes to us with high performance athletes in mind, and usually involves water with appropriate electrolyte, carbohydrate and protein levels for optimising performance in different events under different conditions.
What we can look at when there is little scientific evidence is what is the function of water, what happens when we start to become dehydrated, and what based upon clinical experience is the most appropriate level for most people.