Explain xkcd: It's 'cause you're dumb.
This comic plays on the idea that there is little to no consensus in the scientific community with regard to the amount of water a person should drink per day. In the first panel White Hat presents Cueball with an innocent and sensible suggestion (although controversial) that people should drink six glasses of water per day. In the second panel, more characters joins the discussion, an off-panel voice claims the most common misconception of eight glasses a day, a number which is not supported by scientific research. Ponytail again goes two higher with ten highlighting the existence of a wide range of so-called 'optimum' liquid consumption 'rule-of-thumb'. Implied here is the variety of health-related books, articles, blogs or other literature published that self-proclaims an optimum drinking formula.
The first sign of absurdity also arises here in the second panel when Black Hat posits that we need 5 glasses of water every minute. This equates to 7200 glasses of water a day, and using an often cited "standard definition of a glass", ,  being equal to 8 oz (236 ml), Black Hat is suggesting that we should each drink 1.7 cubic meters (1700 liters) of water a day, not only curing dehydration but also causing water intoxication. This is a typical Black Hat kind of statement that he uses to further emphasizes the absurdity of the problem at hand.
Some time later Megan, despite having read through all studies on dehydration (or low-grade dehydration in particular), still has not come to a solid conclusion. She becomes dizzy, admitting that she's been so focused on her work, she has ironically forgotten to eat or drink. Her personal experience with dehydration prompts someone off-panel to get some water, but since she couldn't find any consensus in her research, she asks how many glasses they should bring her. Presumably to avoid the question of "how many glasses" entirely, Cueball finally suggests that she should drink straight from the tap, a (tenuously) sincere suggestion seeing her dehydration and following the good advice to drink when you are thirsty until that state has been absolved. In the title text of 1744: Metabolism, released less than 3 months after this one, Cueball mentions how he starts to feel bad if he refrains from drinking, just like Megan here. In that comic it is Cueball that tells White Hat about his "problems".
The title text contains a mix-up between two often stated intervals; drinking eight glasses of water per day (which makes no sense, see above) and changing the engine oil every 3000 miles (almost 5000 km) which may be a good rule, but not a necessity. Obviously it's impossible to drink 3000 glasses of water, and changing the oil every eight miles (about 13 km) would make driving a car very impractical.
The subject of this comic has been graphed in 715: Numbers and mentioned in the what if? Soda Planet:
The question of how much water we should drink per day is the subject of furious debate—the "8 glasses" thing seems to be a myth—but the amount of water we actually drink per day seems to be about a liter.
Later, in the what if? Faucet Power, Randall comments on the preference for even numbers in the graph, and writes:
The only real solid advice I've heard is that if you're thirsty, you should drink some water.
How many glasses is "some water" remains an open question...
Beret Guy and Megan are participants of a thought experiment concerning glasses of water and vacuum in the what if? Glass Half Empty.
And the six glasses of water that this comic began with is also mentioned later in 1853: Once Per Day.
This comic is a rare example where a normal few panel comic manages to use five of the seven major characters who actually interact. It is the first comic where Black Hat has spoken (or directly interacted) with White Hat. They have until this comic only appeared together in complicated/large drawings where the two would not need to interact anyway. The only other time this happens is in1881: Drone Training.
- [White Hat and Cueball standing together.]
- White Hat: Many people are mildly dehydrated. And don't realize it. You should drink at least six glasses of water per day.
- [A voice comes from off-panel to the left as Ponytail enters from the left and Black Hat from the right in this frameless panel.]
- Off-panel voice: No, eight glasses!
- Ponytail: I heard ten.
- Black Hat: You need to drink at least five glasses of water per minute.
- [Megan is standing to the left holding a book or a thick binder along her side while holding up a finger with the other hand. A question comes from off-panel to the right. Above her a caption is written in a small frame that breaks the top of this panel's frame:]
- Megan: Okay, I just read through every study I could find to try to figure out whether low-grade dehydration is even a real thing.
- Off-panel voice: What did you learn?
- [Megan looking downwards, has two starbursts a circles and two dots above her head signifying dizziness. Cueball stands to the right as another voice comes from off-panel to the right.]
- Megan: If you spend all day doing research and forget to eat or drink, you start to feel pretty bad.
- Off-panel voice: I'll get some water.
- Megan: But how many glas - Whoa, feeling dizzy.
- Cueball: Maybe you should just drink straight from the tap.
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Uhm, shot glasses or lemonade glasses? Does it have to be a glass or can it be a mug? Could we specify it in litres perhaps?
(How small a glass would you need for 5 glasses a minute in "normal" climate (20 C / 50% RH), without water poisoning? And maybe in 40 C / 15% RH?) --126.96.36.199 14:55, 18 July 2016 (UTC)
I think that's part of the joke, which is itself about how a large amount of people have been informed you should drink x amount of glasses of water per day, but the numbers wildly vary. I'd edit that into the page, but I'm bad at formal language. --188.8.131.52 15:00, 18 July 2016 (UTC)
It is possible to drink too much water, causing a dangerous condition called hyponatremia. Basically you end up dilluting the sodium (and other salts) in your body to a point where many normal functions can't occur. So 3000 glasses a day would probably kill you. On the other hand, I think the difference between a scientific recommendation of 5 and 8 glasses a day is statistically insignificant because other factors (height, weight, metabolism, activity levels, outside temperature, etc.) contribute much more to your needs. Bottom line, it's a lot easier to drink too little water than too much. 184.108.40.206 16:02, 18 July 2016 (UTC)
Of course it would be a WOMAN to get dizzy. #rapeculture 220.127.116.11 (talk) (please sign your comments with ~~~~)
- She's doing SCIENCE, BITCHES. What do you want? 18.104.22.168 18:53, 18 July 2016 (UTC)
The other 'problem' with "you need to drink x amount" of water is the the studies (citation needed) give the amount of water you should consume, which includes the water in all (nonalcoholic)* drinks and food**. I go for days on end without drinking any plain (or carbonated) water without ill effect. There is a reputed way to assess dyhdration which is related to the colour of your "water".
(*)the diuretic effect of alcohol results in the loss of more water than it was drunk with.
(**)no doubt you could devise a diet with lots of juicy veg and fruit but no drinks, but it probably would have too much sugar.RIIW - Ponder it (talk) 18:26, 18 July 2016 (UTC)
Is this the first time White Hat and Black Hat have been in the same comic? 22.214.171.124 19:25, 18 July 2016 (UTC)
- It's the first normal comic to include both. Zach Weiner included both of them in 826, and they were both in 1110: Click and Drag and 1608: Hoverboard. .42 (talk) 20:19, 18 July 2016 (UTC)
- Have you made cross reference between both characters .42? They are also both in 1000 which to my frustration haven't got any categories yet. I swear I will add them someday... but that is also a large comic. Have mentioned the fact in the explanation but with a possible included as I have no citation that it is so. (Yet) --Kynde (talk) 22:22, 18 July 2016 (UTC)
- Oh, I missed 1000. I was only comparing their category pages. .42 (talk) 01:12, 19 July 2016 (UTC)
- Yes and they are not mentioned in 1000, as someone thought that would be too much. I'm not agreing. But you also missed And 1581: Birthday ;-) in which they are mentioned. --Kynde (talk) 09:11, 19 July 2016 (UTC)
- I also looked through and this is indeed the first comic where Black Hat speaks to White Hat. I have made explanation of this fact here. And linked to this from the explanation above. Beret Guy and Black Hat has never spoken together yet, and only once has Beret Guy spoken directly to White Hat. This is also mentioned in the link above. --Kynde (talk) 10:10, 19 July 2016 (UTC)
previous references to drinking n glasses of water a day:
maybe something to be put into the explanation? --126.96.36.199 20:11, 18 July 2016 (UTC)
- Someone has included those two already --Kynde (talk) 22:22, 18 July 2016 (UTC)
is the "maybe you should just drink straight from the tap" is related to the person saying "i'll get some water" being black hat. no one wants that. --188.8.131.52 11:35, 19 July 2016 (UTC)
- Funny detail, but since we do not know how much later we also do not know who is still there. Anyway if you are thirsty just drink from the tap, that saves the counting of glasses which was the point. --Kynde (talk) 21:37, 19 July 2016 (UTC)
I heard that the fuller quote is 'We need x glasses of water per day, most of which comes from our food'. 184.108.40.206 (talk) (please sign your comments with ~~~~)
- Yes, this. Elvenivle (talk) 02:11, 20 July 2016 (UTC)
It's my understanding that the ideal amount of water to drink is gauged by however much it takes to turn your urine clear, which would undoubtedly vary from person to person. 220.127.116.11 05:35, 20 July 2016 (UTC)
- um, a-level chemistry flooding back, i think you mean colourless. if your urine is cloudy you're in trouble. if it is dark brown then all that happens is that people who subscribe to the belief that this is harmful in some way get alarmed. for every imaginary study they have pointing out how harmful this is i have three that show it isn't and the opposite is true, that putting unnecessary pressure on your kidneys will have Dire Results. --18.104.22.168 12:09, 20 July 2016 (UTC)
- 22.214.171.124 has the right idea, colorless urine = "you're drinking enough", yellow urine = "you should drink more" 126.96.36.199 (talk) (please sign your comments with ~~~~)