We seem to be told constantly to ‘drink at least 2L of water a day’ or ‘8 large glasses of water a day’, so much so that I used to feel guilty if I wasn’t carrying a drink bottle with me all day, constantly sipping from it, and rating the colour of my wee on a hydration scale. It became a full time job. So I was pretty relieved to hear that the scientific proof behind this is lacking.
Why are we told this? There is a theory that a doctor said it flippantly one day back in the 70’s and it then took off in the form of marketing by water companies. The truth is, no-one knows, and there are no scientific articles that support it.
So how much should we drink? Without getting too complicated, many dieticians and physiologists suggest 30ml of FLUID (including caffeinated drinks, fizzy drinks, water, soups) per kg of body weight, per day. This should mostly be water. So, if you’re 60kg, that’s 1.8L a day, including all your drinks/smoothies/soups. Bear in mind that this is for a healthy adult, in a temperate climate performing mild exercise. If you’ve run a marathon, sweated out a river on a hot day, are on a long-haul flight, drank a coupley botts last night or have some specific diseases, you should probably have a few extra glasses of water.
Water in our diet is important for things like avoiding constipation and it is crucial in our basic body functioning. However, the enforced guilt of not drinking enough water is unsubstantiated and may, in fact be harmful due to dilution of important vitamins and minerals, undue strain on the kidneys and is setting you up with poor bladder habits. It’s a bit of a balancing act, but many of my patients are drinking too much water (causing leakage of urine and having to rush to the toilet often) or too little (causing constipation, urgency to wee, and dehydration). I encourage you to do the math above, measure out your liquid for a day to see how much fluid it takes to reach your quota, and try to stick to that.
If you want more information, refer to the following article by Heinz Valtin, a retired professor of physiology who specialises in kidney research:
Heinz, Valtin (2002) “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 × 8”?American Journal of Physiology, Vol. 283 no. 5, R993-R1004
– the vagina physio