The body comprises approximately 60% water. It is an essential requirement for the body to function. For example, it maintains our temperature, provides lubrication for the joints, and helps to rid the body of waste. It also helps to maintain healthy concentration levels. Overall, the amount of water we drink is essential for our wellbeing. In this article, I will discuss how much water we should drink daily and the science behind it.
We should drink ‘8’ glasses of water a day.
It is common to hear that we need eight glasses of water today – about two litres (or 8 x 8 oz glasses of water). There is, in fact, no scientific evidence for this requirement. The source of this may be a 1945 recommendation by the US National Research Council (NRC). The recommendation said that adults should consume 1 millimetre of water for each calorie of food which means about 2.5 litres per day for men and two litres for women.
This ‘rule’ may work for some, but most people do not realise the amount of water we get from food. Food contains water and is broken down chemically into carbon dioxide and water. Some estimates suggest we get 20 – 30 % of our daily needs from food. For example, strawberries contain 90 – 99% of water. Bananas contain 70 – 79% water, and chicken breast contains 60 – 69% water.
On this basis, you will need less than eight servings of eight ounces of water daily.
As a more quantitative measure, we can estimate the amount of water we need on a daily basis by multiplying our weight by 0.033. This will translate into the number of litres of water we should drink every day.
That said, the best indicator of whether we are hydrated or not is our ‘thirst’ and the subtle signals that the body provides us in order to quench it.
How much water should we drink every day?
So, what happens in the body that signals the need to drink? Until recently, the precise mechanism by which this happens was unknown.
Recent research suggests that thirst has a sensory system similar to seeing or hearing. Many signals govern the regulation of thirst throughout the body. These signals arise from the mouth, gut and blood. They enable every cell in the body to reliably inform the brain about the body’s current hydration levels.
The convergence of the thirst sensory system occurs in a part of the brain that governs thirst. From here, the brain determines a real-time estimate of the body’s water needs. The body then responds physiologically with the urge to drink, amongst other things.
Should we drink during our meals?
Some traditions suggest that we should not mix food and water. The hypothesis is that water dilutes stomach acid levels. It makes sense conceptually. Adding water to something acidic will reduce its acidity.
But does this correspond to what is happening physiologically? Research suggests that eating triggers additional signals relating to fluid intake. The sensory nodes send signals to the brain in advance of the absorption of food. This activity drives fluid consumption during eating (known as ‘prandial drinking’). If water is unavailable, this may suppress eating. This shows that there are neural pathways that regulate the consumption of eating and drinking.
So, the conclusion that eating whilst drinking harms digestion is questionable.
The role of swallowing and urine colour.
Interestingly enough, swallowing controls the amount of fluid intake. If you are dehydrated, swallowing is effortless. If you’re over hydrated, swallowing feels difficult.
A study suggests that areas of the brain associated with conscious thought processes are more active when the body is overhydrated. It implies that when the body’s hydration levels reach their optimal level, the body will physically inhibit fluid intake.
The darker the colour of the yellow urine, the more dehydrated we are. If we are significantly dehydrated, our urine will be dark brown or orange as there isn’t enough water to dilute the urea. Water acts as a function of removing waste from the body. So if there is less water, the colour will become more concentrated.
Likewise, if there is no colour or it is transparent, it may indicate too much fluid intake. Other factors may contribute to a darker urine colour, such as the intake of B vitamins.
So, whilst in mindfulness, we emphasise that we shouldn’t pay too much attention to our thoughts. However, when it comes to drinking, it is a different story. Our bodies will tell you us when we need to drink and how much. So whilst we can stick to a rough guide of 8 glasses a day, such measurement isn’t practical or accurate. Rather, listen to the subtle signals our brain will give when it’s time to drink. That’s a much more precise method.
If I can help you with your wellbeing, please feel free to get in touch to discuss your goals or needs, or email me at firstname.lastname@example.org
Rhiannon Lambert, The Science of Nutrition, DK, Great Britain, 2021.
Christopher Zimmerman, The origins of thirst, Science, 2 October, 2020.
Claire Wilson, How much water should you drink a day? Your throat will tell you, New Scientist, 10 October, 2016.
Graham Lawton, Good hydrations: Do I need eight glasses of water a day?, New Scientist, 8 March, 2017.
Eleanor Horton, How does water hydrate us? New Scientist, 28 August, 2019.