Eight Glasses of Water?

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Eight glasses of water? - by Roxana Soetebeer

We often hear the advice to drink eight glasses of water per day, but have you ever wondered where this recommendation originated and whether it holds up to scientific scrutiny? The idea of consuming eight glasses of water daily dates back to 1945 when the Food and Nutrition Board of the National Academy of Sciences suggested that, on average, an adult male requires around 2500 calories per day. Following this suggestion, they proposed that one should also consume 1 ml of water for each calorie consumed. Hence, the initial claim was to drink 2500 ml of water daily, equivalent to eight 8-ounce glasses.

However, this claim was built on two significant assumptions that merit closer examination.

First, it assumed that everyone needs 2500 calories a day, irrespective of their unique physiological and metabolic factors. In reality, individual caloric requirements vary significantly based on factors such as age, sex, weight, genetics, lifestyle, and physical activity levels. So, the idea of a uniform water intake for all is questionable at best.

Second, the assumption is that our only source of water comes from the tap. In reality, water is in most foods we eat. Consider the example of a potato. While an average-sized potato contains approximately 110 calories, it comprises around 79% water when raw and 77% water when cooked. Consuming a potato provides energy through its caloric content and contributes to your overall water intake. So, we would subtract any amount of water in the potato from the 2500 daily millilitres. This phenomenon applies to various fruits and vegetables, highlighting the need for a more nuanced understanding of water consumption beyond just drinking plain water.

Before the "eight glasses of water" concept became widespread, humans were never accidentally dying of dehydration. So, why is this? Our bodies have a remarkable natural mechanism to regulate water balance: Thirst. It is the indicator of when and how much we should drink. We know this has worked since, before 1945, there wasn't mass dehydration. Because we have this natural regulation of when we need water, there is no need for a mandated amount—we don't need a number. 

Next, we should analyze the possible adverse effects of excessive water consumption. Beyond the obvious that consuming too much water too quickly is called drowning, we should look at water toxicity. While the risks of dehydration are widely recognized, the hazards of over-hydration, known as water toxicity or water intoxication, are less discussed. This condition occurs when someone drinks an excessive amount of water in a short period, overwhelming the body's ability to balance electrolytes.

The general guideline for daily water intake to avoid water toxicity is around 3700 ml for males and 2700 ml for females. Already this should look concerning. 2500 ml vs 2700 ml isn't a huge gap. Especially when the "eight glasses of water" statement has become so sensationalized that it isn't often mentioned that eight cups is only the recommendation for males. When this idea is irresponsibly spread an extra 200 ml of water might not seem like much, but it can put a lot of people at risk of water toxicity. This becomes especially egregious when the symptoms range from nausea to coma and death.

In conclusion, the belief that one must drink eight glasses of water a day has been ingrained in our minds for decades. However, when we examine its origins and assumptions, we find that it lacks a strong scientific basis. The idea was initially based on an average calorie intake, overlooking the fact that individual caloric needs vary significantly based on genetics, lifestyle, and other factors. Additionally, the assumption that water can only come from the tap neglects the significant water content present in the foods we eat.

Final thought: If you experience an unusual or unquenchable thirst, please contact your medical provider to rule out significant health problems.

Written by Roxana Soetebeer MHP
Published August 5th, 2023

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