Water is obviously the major constituent of our body mass but also blood which carries not only oxygen in the haemoglobin (which gives blood the red colour) but also heat, nutrients, hormones etc. Water is also important in digestion and helps us to avoid constipation. Water is also important to keep the kidneys functioning and there is some evidence that drinking a bit more water helps avoid urinary tract infections in women. Dehydration can occur in many illnesses and when we have a fever or diarrhoea we can lose a great deal of water through the skin and gut which needs replacing to not only maintain blood pressure etc. but to maintain electrolyte balance – mainly sodium. Rehydration powders can help but are very salty and might actually put one off drinking more whereas there is evidence that apple juice diluted 50:50 is effective and far more palatable.
In the US, popular advice is to drink eight, 8-ounce glasses of water or approximately two litres daily. This “8×8 rule” originated from a recommendation by Dr Fredrick J Stare in 1974. His actual recommendation was actually “six to eight glasses” and in the UK, the NHS recommends this or up to 1.2 litres of “fluids” daily, pointing out that we also get significant amounts of water from our food especially fruit, salads and vegetables.
There is no medical evidence that drinking that much water is beneficial to your health. Prospective studies fail to find benefits in kidney function or all-cause mortality when healthy people increase their fluid intake. Randomized controlled trials fail to find benefits as well, with the exception of specific cases — for example, preventing the recurrence of some kinds of kidney stones.
How much water one actually needs to drink is governed how active you are, the weather (sweating) and your individual physiology and current health. Real dehydration, when your body has lost a significant amount of water because of illness, excessive exercise or sweating, or an inability to drink, is a serious issue. But people with clinical dehydration almost always have symptoms of some sort.
How many of us are seriously dehydrated? Galloway studied fluid intake among call-centre workers and found that, to keep their ratings up, many would restrict their fluid intake to avoid toilet breaks. Long distance truck drivers etc. might be expected to behave similarly.
If we’re ingesting enough water, he adds, we should probably be going to the bathroom “somewhere between five and seven times a day”.
In 2017, The Mayo Clinic noted that:
“Most healthy people can stay hydrated by drinking water and other fluids whenever they feel thirsty. For some people, fewer than eight glasses a day might be enough. But other people might need more.”
The Mayo Clinic recommends taking in between 2 — 3 Litres (or more) per person per day, depending on activity level and whether the individual is male or female, they specifically note that this is fluid from all sources to include coffee, tea, and other beverages, as well as water intake from fruits and vegetables. Essentially the evidence from the Mayo Clinic and others suggests that we need to replace exactly as much water as we lose. There are averages, of course, but individual needs will vary.
In 2016, Galloway tested the hydrating potential of a range of drinks and found a litre of beer was no less hydrating than a litre of water. Similarly, a litre of instant coffee, containing 212mg of caffeine, was as hydrating as water.
Milk was even more hydrating and effective as a hydration solution for people with diarrhoea. So even diuretics such as coffee, tea and alcoholic drinks, although they might make us visit the bathroom more often don’t actually dehydrate us.
However although the advice of sticking to the “8×8 rule” can’t be substantiated by scientific evidence it is possible to drink too much or too little and so there must be caveats to the assumption that our thirst etc. will drive us to maintain our hydration. For example patients with dementia may become dehydrated if they’re unable to communicate or recognise that they’re thirsty, or if they forget to drink. This can lead to headaches, increased confusion, urinary tract infections and constipation and can have a negative effect on the signs and symptoms of dementia.
So in summary so long as you are not getting thirsty and are visiting the WC half a dozen times a day or so you are likely well hydrated and don’t need to adjust your fluid intake. Also the good news is that coffee, tea, milk, beer and juices are all good sources of water.
Have a drink of whatever you fancy and keep hydrated!
…and just to finish, the environment outside your body is important too!