How much water should you be drinking? If you think that's a simple question, think again. There's a bewilderingly wide range of opinions on this subject and advice seems to be changing all the time. So how much is enough, and how much is too much?
We're rather wet creatures. In fact, a healthy human is over 66% water. Nearly all of the chemical reactions in our cells - chemical reactions involved in such processes as growth and tissue repair – need water. Our bloodstream is just that, a stream, essential for transporting nutrients around the body and getting rid of waste.
Our water supplies have to be topped up constantly, to make up for the fluid we lose when we breathe, sweat and urinate. A lack of sufficient fluid intake has been linked to all sorts of manifestations of ill health, including headaches, slowed mental processes, poor sleep, digestive problems and greater susceptibility to infection. Conversely, getting enough water is an apparently sure-fire way of improving your energy levels, controlling your weight and even preventing wrinkles.
But how much is enough? And does it have to be water? Ubiquitous in standard government guidelines here and in Europe and America is the eight-glasses-a-day rule. A glass is assumed to equate to 200 ml and the standard recommendation is that women should drink around 1.6 litres a day and men around 2 litres. And it doesn't have to be water, we're told. Tea, coffee, fruit juices and milk all count (though alcohol and fizzy drunks do not, as they have diuretic properties, taking more fluid out of the body than they put in.)
So it's simple, right? Eight glasses a day and we'll be fine.
Not so fast...
First of all, some diet and nutrition experts are saying that we actually need far more water than this. For the purposes of weight loss and general “detox,” in particular, at least 3 litres of water or herbal tea (not, generally, tea or coffee or fruit juices) a day are often recommended. There is a considerable body of anecdotal evidence in this domain – many people swear by the life-boosting properties of a habit of constant water-drinking throughout the day. The benefits mentioned most often are weight loss, improved digestion, better skin, greater ability to concentrate and increased energy levels. Many people find that habitually troublesome headaches disappear when they consume 3 litres of water a day or more, and some also report improved mood and immunity. What's not to like? Let's get glugging!
Sorry, no, it's not that simple either...
On the other side of this debate are the water sceptics. Their arguments goes something like this: Yes, of course we need water to survive. But the body is an amazingly adaptive organism that can make up for fluctuations in water consumption via the mechanisms of urination and sweating, and it's possible to get plenty of fluid from the food we eat, particularly fruit and vegetables. For most of its existence across history and in more places than not around the world today, human beings are not, generally, drinking over 3 litres of water a day, and we seem to be managing just fine. And you need to look carefully at where the drink-more-message is coming from: very often, it's producers of sports drinks or bottled water who are urging us to drink (read: consume) more.
And it gets worse: It is possible to drink too much water. Or at least, to drink too quickly. Our kidneys can handle 15 litres of water a day, and you're very unlikely to manage that. But if you drink a lot of water over a short period of time (perhaps trying to meet that 3 litre target in the half an hour before bedtime), there's a risk of suffering water intoxication. This occurs when the body's sodium levels are dangerously diluted and can be fatal. Some medical and dietary experts have also voiced concern about more benign levels of over hydration, the symptoms of which include clear urine, frequent night urination, cold extremities, problems with cognitive and emotional functioning and, paradoxically, seemingly unquenchable thirst.
So how can we possibly get our water consumption right, faced with all this conflicting advice?
The simplest thing is to pay attention to your body and to trust in its signals rather than in some standard guideline. Notice how often you urinate, and how concentrated your urine is. If you're prone to headaches and energy slumps, try increasing your water consumption but don't take it to extremes. If you're one of those people who lugs a 2-litre bottle around everywhere and tops it up several times a day, consider whether you might be consuming too much.
In essence, don't let yourself get too thirsty but if you’re not thirsty, don’t drink a lot of water.