2 ½ litres of water per day - really?

Many people I know drink water constantly – they are always taking a swig out of a water bottle that never leaves their side. After having renal stones recently, I tend to try to drink more, but just don’t like drinking water, and I find that I am not thirsty most of the time anyway. Who’s right – those who tell me to drink water constantly, or my body, which rarely makes me feel thirsty?

The origins of the “at least 8 glasses of water per day” recommendation have been traced in this article (here) and it appears that they are not based on any scientific studies (summarised here). One origin (but not the only one) was a 1945 US Food and Nutrition Board of the National Research Council recommendation that the average adult needs 2.5 litres of water per day. Scientifically, that statement is correct, but that is a long way from saying that we need to drink 2.5 litres of water. In fact, the report goes on to (correctly) state that “most of this quantity is contained in prepared foods”.

Not only is the recommendation to drink 2.5l of water per day not supported by science, it appears that the intake recommendations have crept up over time (from “between 6 and 8 glasses”). Also, and more importantly, water intake from other sources appears to have been disregarded. As noted above, most of our water input comes from food and non-water beverages (coffee, milk, juice, beer etc.). A good summary of the topic (and a look at our daily water input/output) by Dr Karl (well known to Australian audiences) can be found here.

Yet the persistence of this myth has been remarkable. Probably because it is simple and superficially appealing: it sounds good. More than that, it sounds healthy. Readers of this blog know how pervasive and attractive theories that ‘sound good’ can be. An appealing simplification will often win out over a scientific explanation.

Not only is the recommendation unsustained scientifically, it is also potentially harmful. It is rare, but there are cases of people dying from drinking too much water (here, here and a famous case of a lady that died after a water drinking contest in Sacramento, here).

Yet campaigns to promote drinking water continue, the overdiagnosis of dehydration persists and the penetration of the culture of carrying water bottles and constantly drinking has increased, rather than decreased (here).

The bottom line

A recommendation that was never based on science, and was misinterpreted form the start has become common ‘knowledge’. The water intake myth has such great superficial appeal that it proven to be resistant to attempts to dismantle it. Me? I drink when I am thirsty, plus maybe a little more because of my history of kidney stones, but rarely do I drink plain water. Now, if only I could restrict my eating to when I am hungry.