The health authorities commonly recommend eight 8-ounce glasses, which equals about 2 liters, or half a gallon. This is called the 8×8 rule and is very easy to remember.
However, there are other health gurus who think we’re always on the brink of dehydration and that we need to sip on water constantly throughout the day… even when we’re not thirsty.
As with most things, this depends on the individual and there are many factors (both internal and external) that ultimately affect our need for water.
I’d like to take a look at some of the studies on water intake and how it affects the function of the body and brain, then explain how to easily match water intake to individual needs.
Can More Water Increase Energy Levels and Improve Brain Function?
Many people claim that if we don’t stay hydrated throughout the day, our energy levels and brain function can start to suffer.
There are actually plenty of studies to support this.
Bottom Line: Mild dehydration caused by exercise or heat can have negative effects on both physical and mental performance.
Does Drinking a Lot of Water Help You Lose Weight?
There are many claims about water intake having an effect on body weight… that more water can increase metabolism and reduce appetite.
Bottom Line: Drinking water can cause mild, temporary increases in metabolism and drinking it about a half hour before meals can make people automatically eat fewer calories.
Cancer: There are some studies showing that those who drink more water have a lower risk of bladder and colorectal cancer, although other studies find no effect.
Kidney stones: Increased water intake appears to decrease the risk of kidney stones.
Acne and skin hydration: There are a lot of anecdotal reports on the internet about water helping to hydrate the skin and reducing acne, but I didn’t find any studies to confirm or refute this.
Bottom Line: Drinking more water may help with several health problems, such as constipation and kidney stones.
Plain water is not the only thing that contributes to fluid balance, other drinks and foods can also have a significant effect.
Most foods are also loaded with water. Meat, fish, eggs and especially water-rich fruits and vegetables all contain significant amounts of water.
If you drink coffee or tea and eat water-rich foods, then chances are that this alone is enough to maintain fluid balance, as long as you don’t sweat much.
Bottom Line: Other beverages that you drink also contribute to fluid balance, including caffeinated drinks like coffee and tea. Most foods also contain water.
Maintaining water balance is essential for our survival.
For this reason, evolution has provided us with intricate mechanisms for regulating when and how much we drink.
When our total water content goes below a certain level, thirst kicks in.
This is controlled by mechanisms similar to things like breathing… we don’t need to consciously think about it.
For the majority of people, there probably isn’t any need to worry about water intake at all… the thirst instinct is very reliable and has managed to keep us humans alive for a very long time.
There really is no actual science behind the 8×8 rule. It is completely arbitrary.
That being said, there are certain circumstances that may call for increased water intake… that is, more than simple thirst commands.
The most important one may be during times of increased sweating. This includes exercise, as well as hot weather (especially in a dry climate).
If you’re sweating a lot, make sure to replenish the lost fluid with water. Athletes doing very long, intense exercises may also need to replenish electrolytes along with water.
Water need is also increased during breastfeeding, as well as several disease states like vomiting and diarrhea.
Older people may need to consciously watch their water intake, because some studies show that the thirst mechanisms can start to malfunction in old age.
How Much Water is Best?
At the end of the day, no one can tell you exactly how much water you need. As with most things, this depends on the individual.
If you want to keep things simple (always a good idea), then these guidelines should apply to 90% of people:
When thirsty, drink.
When not thirsty anymore, stop.
During high heat and exercise, drink enough to compensate for the lost fluids.