John_Maxwell_IV and I were recently wondering about whether it's a good idea to try to drink more water. At the moment my practice is "drink water ad libitum, and don't make too much of an effort to always have water at hand". But I could easily switch to "drink ad libitum, and always have a bottle of water at hand". Many people I know follow the second rule, and this definitely seems like something that's worth researching more because it literally affects every single day of your life. Here are the results of 3 minutes of googling:

http://www.sciencedirect.com/science/article/pii/S0002822399000486:

Dehydration of as little as 1% decrease in body weight results in impaired physiological and performance responses (4), (5) and (6), and is discussed in more detail below. It affects a wide range of cardiovascular and thermoregulatory responses (7), (8), (9), (10), (11), (12), (13) and (14).

The Nationwide Food Consumption Surveys indicate that a portion of the population may be chronically mildly dehydrated. Several factors may increase the likelihood of chronic, mild dehydration, including a poor thirst mechanism, dissatisfaction with the taste of water, common consumption of the natural diuretics caffeine and alcohol, participation in exercise, and environmental conditions. Dehydration of as little as 2% loss of body weight results in impaired physiological and performance responses. New research indicates that fluid consumption in general and water consumption in particular can have an effect on the risk of urinary stone disease; cancers of the breast, colon, and urinary tract; childhood and adolescent obesity; mitral valve prolapse; salivary gland function; and overall health in the elderly. Dietitians should be encouraged to promote and monitor fluid and water intake among all of their clients and patients through education and to help them design a fluid intake plan.

The effect of dehydration on mental performance has not been adequately studied, but it seems likely that as physical performance is impaired with hypohydration, mental performance is impaired as well (62) and (63). Gopinathan et al (29) studied variation in mental performance under different levels of heat stress-induced dehydration in acclimatized subjects. After recovery from exercise in the heat, subjects demonstrated significant and progressive reductions in the performance of arithmetic ability, short-term memory, and visuomotor tracking at 2% or more body fluid deficit compared with the euhydrated state.

So how much is 2% dehydration? http://en.wikipedia.org/wiki/Dehydration#Differential_diagnosis : "A person's body, during an average day in a temperate climate such as the United Kingdom, loses approximately 2.5 litres of water.[citation needed]" http://en.wikipedia.org/wiki/Body_water quotes Arthur Guyton 's Textbook of Medical Physiology: "the total amount of water in a man of average weight (70 kilograms) is approximately 40 litres, averaging 57 percent of his total body weight." So effects on cognition become apparent after 40l*2%=800ml of water has been lost, which takes roughly 800ml/(2.5l/24h) = 8 hours. Now, this assumes water is lost at a constant rate, which is false, but it still seems like it would take a while to lose a full 800ml. Which implies that you don't have to make a conscious effort to drink more water because everybody gets at least mildly thirsty after, say, half an hour of walking around outside on a warm day, which seems like it would be a lot less than 800ml.

http://freebeacon.com/michelle-obamas-drink-more-water-campaign-based-on-faulty-science/ : “There really isn’t data to support this,” said Dr. Stanley Goldfarb of the University of Pennsylvania. “I think, unfortunately, frankly, they’re not basing this on really hard science. It’s not a very scientific approach they’ve taken. … To make it a major public health effort, I think I would say it’s bizarre.” Goldfarb, a kidney specialist, took particular issue with White House claims that drinking more water would boost energy. ”The idea drinking water increases energy, the word I’ve used to describe it is: quixotic,” he said. “We’re designed to drink when we’re thirsty. … There’s no need to have more than that.”

http://ask.metafilter.com/166600/Drinking-more-water-should-make-me-less-thirsty-right : When you don't drink a lot of water your body retains liquid because it knows it's not being hydrated. It will conserve and reabsorb liquid. When you start drinking enough water to stay more than hydrated your body will start using the water and then dispensing of it as needed. Your acuity for thirst will be activated in a different way and in a sense work better.

Some thoughts:

• More frequent water-drinking makes you urinate more often, which is probably a bad thing for productivity.
• There might be negative effects with chronic mild dehydration at levels less severe than in the studies above.
• There might also be hormetic effects. (As in, your body functions best under frequent mild dehydration because that's what happened in the EEA, and always giving it as much water as it wants will be bad.)

Thoughts? Please post your own opinion if you're knowledgeable about this or if you've researched it.