It's not just that it's critical to survival. It's quite critical to health in the following ways: * A guard against hangovers. If you drink enough water while going out, your hangover will be minimal. The suggestion is to chug a 8-12oz water glass with every drink, and that's what I do. Say at a bar, I order a beer, and also water, chug the water, then sip the beer. Do it between 9pm-3am, not have a terrible hangover in the morning. Without water tho, your hangover will be so much worse. * Better sleep and shorter sleep requirement! I just kind of discovered it recently, and still subject to validation. If you go to sleep well-hydrated, you need to sleep less to recover your energy. It's a time saver! * SypherPK, a twitch streamer, notes that being well-hydrated reduces perceived eye strain for him (he spends tens of hours a day at his computer). I haven't verified or perceived this. * Hopefully, really hopefully drinking lots of water should prevent headaches. I say that because I feel that I'm at risk of getting more headache due to the nature of work I do (a software engineer in Chicago). So there is that. Water. It's important.