Regulatory, Integrative and Comparative Physiology

“Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 × 8”?

Heinz Valtin,


Despite the seemingly ubiquitous admonition to “drink at least eight 8-oz glasses of water a day” (with an accompanying reminder that beverages containing caffeine and alcohol do not count), rigorous proof for this counsel appears to be lacking. This review sought to find the origin of this advice (called “8 × 8” for short) and to examine the scientific evidence, if any, that might support it. The search included not only electronic modes but also a cursory examination of the older literature that is not covered in electronic databases and, most importantly and fruitfully, extensive consultation with several nutritionists who specialize in the field of thirst and drinking fluids. No scientific studies were found in support of 8 × 8. Rather, surveys of food and fluid intake on thousands of adults of both genders, analyses of which have been published in peer-reviewed journals, strongly suggest that such large amounts are not needed because the surveyed persons were presumably healthy and certainly not overtly ill. This conclusion is supported by published studies showing that caffeinated drinks (and, to a lesser extent, mild alcoholic beverages like beer in moderation) may indeed be counted toward the daily total, as well as by the large body of published experiments that attest to the precision and effectiveness of the osmoregulatory system for maintaining water balance. It is to be emphasized that the conclusion is limited to healthy adults in atemperate climate leading a largely sedentaryexistence, precisely the population and conditions that the “at least” in 8 × 8 refers to. Equally to be emphasized, lest the message of this review be misconstrued, is the fact (based on published evidence) that large intakes of fluid, equal to and greater than 8 × 8, are advisable for the treatment or prevention of some diseases and certainly are called for under special circumstances, such as vigorous work and exercise, especially in hot climates. Since it is difficult or impossible to prove a negative—in this instance, the absence of scientific literature supporting the 8 × 8 recommendation—the author invites communications from readers who are aware of pertinent publications.

  • fluid intake
  • optimal fluid intake
  • daily water intake
  • water balance


  • The friendly, helpful staff and atmosphere of the Biomedical Libraries at Dartmouth, directed by W. Garrity, invite full use of the superb facilities. R. M. Barton, Statistical Consultant, Peter Kiewit Computing Services at Dartmouth College, gave invaluable help in extracting and analyzing information from government documents on CD-ROM, data that would otherwise have been indecipherable to me.

  • I am indebted to the following persons for help and advice: S. G. Dentzer, J. T. Du, M. Durand, M. Goodrich, D. C. Grossman, K. E. Heller, D. J. Izzo, M. A. Knepper, T. L. Mead, R. P. Mogielnicki, D. J. Ramsay, and G. L. Robertson.


  • Because our search for scientific evidence in support of the dictum that we “…drink at least eight glasses of water a day” came up empty, it seems important to list here the various approaches we used in our efforts to find pertinent articles.

  • Electronic Searches

  • Many electronic databases were explored, including MEDLINE, BIOSIS Previews, CAB Abstracts, Science Citation Index, ABI/INFORM Global through ProQuest Direct, the World Wide Web, the OCLC Union Catalog through WorldCat, and the Research Libraries Group Union Catalog. “Drinking,” “water—administration and dosage,” and “optimal fluid intake” are examples of terms and phrases searched. The last led us to the article by Dr. A. Grandjean (40) and got us started on the pertinent scientific literature.

  • Nutritionists

  • In the absence of scientific articles, personal contacts with nutritionists turned out to be the best resource. Having conducted similar searches in vain, these nutritionists were frustrated by the perpetuation of 8 × 8 and offered tremendous help freely. They were Dr. Abby G. Ershow (Nutrition Program Officer, National Heart Lung Blood Institute, NIH), Dr. Ann C. Grandjean (Executive Director, Center for Human Nutrition, University of Nebraska Medical Center), Dr. Barbara J. Rolls (Guthrie Chair, Department of Nutrition, Pennsylvania State University), Dr. Elizabeth M. Whelan (President, American Council on Science and Health), Dr. Allison A. Yates (Director, Food and Nutrition Board, National Academy of Sciences), and Dr. Paula R. Trumbo (Senior Program Officer, Food and Nutrition Board, National Academy of Sciences).

  • Colleagues

  • Personal inquiries with ∼15 colleagues who specialize in the area of water balance resulted in prompt responses. None of them knew the origin of 8 × 8 nor (with one possible exception) of published articles that support the claim. The possible exception was Dr. Lise Bankir, whose views have been described under possible benefits of a high water intake: Speculative Advantages. Because naming these colleagues might draw them into the controversy over 8 × 8 without their permission, I will not list them here; however, they know who they are and I thank them for their efforts.

  • Authors of Lay Articles

  • I received no replies from three authors of lay articles whom I had asked for the sources and scientific evidence for their assertions and recommendations.

  • Address for reprint requests and other correspondence: H. Valtin, Dept. of Physiology, Dartmouth Medical School, Borwell Bldg., 1 Medical Center Dr., Lebanon, NH 03756-0001 (E-mail:heinz.valtin{at}

  • August 8, 2002;10.1152/ajpregu.00365.2002

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