ברכות מ, א
אָמַר רָבָא בַּר שְׁמוּאֵל מִשְּׁמֵיהּ דְּרַבִּי חִיָּיא … וְאַחַר כׇּל שְׁתִיָּיתְךָ שְׁתֵה מַיִם וְאִי אַתָּה נִזּוֹק. תַּנְיָא נָמֵי הָכִי:… שְׁתֵה מַיִם וְאִי אַתָּה נִזּוֹק.
תָּנוּ רַבָּנַן: הַמַּקְפֶּה אֲכִילָתוֹ בְּמַיִם, אֵינוֹ בָּא לִידֵי חוֹלִי מֵעַיִם. וְכַמָּה? אָמַר רַב חִסְדָּא: קִיתוֹן לְפַת
And Rava bar Shmuel said the following advice in the name of Rabbi Chiyya: …after all drinking, drink water and you will not be harmed. That was also taught in a baraita: … drink water and you will not be harmed.
On the topic of health, the Gemara cites that the Sages taught in a baraita: One who inundates his food with water, i.e., one who drinks a great deal of water, will not come to suffer from intestinal illness. The Gemara asks: And how muchwater? Rav Chisda said: One jug [kiton] per loaf.
There are a lot of myths in medicine. You only use 10% of your brain. (Nope). Reading in dim light ruins your eyesight (not even close). And you should drink at least eight glasses of water a day. Also nonsense.
THe origins of the eight cups per day mantra
It is not clear where the modern myth that a person needs to drink eight cups of water each day originated. In a 2002 review of the topic, Heinz Valtin from Dartmouth Medical School suggested that it may have began with “the renowned nutritionist” Fredrick J. Stare, who was an early champion of drinking at least six glasses of water a day. In 1974 Stare wrote this:
How much water each day? This is usually well regulated by various physiological mechanisms, but for the average adult, somewhere around 6 to 8 glasses per 24 hours and this can be in the form of coffee, tea, milk, soft drinks, beer, etc. Fruits and vegetables are also good sources of water.
OK, so a couple of things to note. First, there is no reference for this assumption. It is just asserted, which isn’t the way medical recommendations should be made. Second, Stare wrote that the water need not be drunk from a glass. “Fruits and vegetables are also good sources of water.” Third, there is a huge difference between “somewhere around 6 to 8 glasses” and “at least eight glasses.” And fourth, Stare’s original claim allowed for coffee, tea, soft drinks, and even beer. But proponents of the eight glasses a day mantra do not permit these other beverages as part of their eight cups per day regimen.
In fact the recommendation may go further back that Dr Stare. In 1945 the Food and Nutrition Board of the National Research Council wrote:
A suitable allowance of water for adults is 2.5 liters daily in most instances. An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods.
According to Valtin from Dartmouth, that the last sentence was ignored, “and the recommendation was therefore erroneously interpreted as eight glasses of water to be drunk each day.”
No, You don’t need to Drink eight cups of water each day
So much for the history. What evidence is there to support the claim? Not much. Consider for example, a very large study in the Netherlands in the 1980s and published in the British Journal of Nutrition in 2010. Researchers followed over 120,000 individuals for a period of 10 years, and studied the relationships between fluid intake levels and mortality from heart attack and stroke. They found no link between total fluid intake or water intake and either cause of mortality. They also reported that coffee consumption was inversely associated with mortality from ischemic heart disease in women only, while a higher tea intake was associated with lower mortality in men only. So basically, tea and coffee are sexist.
Fluids don’t do much for your kidney function, and there is no evidence that coffee makes you dehydrated. Also, according to Israeli dermatologists, they don’t do anything for your looks. Sorry.
We have discussed the terrible state of nutrition research before, and noted that for many foods there are conflicting recommendations about whether or not they are good for you. Water is no different, and so it is no surprise to find a study that suggests drinking lots of water is indeed beneficial. In 2002 the American Journal of Epidemiology published the results of the Adventist Health Study, which had followed over 20,000 people since the mid 1970s. Among the findings were that high daily intakes of water (five or more glasses) compared with low (two or fewer glasses) were associated with a decreased risk of heart disease in both men (RR=0.46 95% confidence interval (CI): 0.28, 0.75;) and women, (RR= 0.59 95% CI: 0.36, 0.97). Also, A high fluid intake is associated with a decreased risk of bladder cancer in men. Maybe.
“How-to books, beauty journals, the Internet, and the media usually recommend drinking six to eight glasses of water each day for keeping the skin hydrated, helping it look healthier, and making it less prone to wrinkles. We have found no scientific proof for this recommendation; nor is there proof, we must admit, that drinking less water does absolutely no harm. The only certainty about this issue is that, at the end of the day, we still await scientific evidence to validate what we know instinctively to be true—namely, that it is all a myth.”
Having now studied today’s page of Talmud we are able to add to the important literature on the origins of the eight cups per day myth. It didn’t start in the 1970s or even the 1940s. It began with Rabbi Chiyya in the Babylonian Talmud, and his recommendation to drink a jug of water with every loaf of bread.
“ הנה ימים באים נאם אדני יהוה והשלחתי רעב בארץ לא רעב ללחם ולא צמא למים כי אם לשמע את דברי יהוה
A time is coming—declares my Lord God—when I will send a famine upon the land: not a hunger for bread or a thirst for water, but for hearing the words of the Lord.”
