My brother is a badass. When he went to boot camp for the Army, he said that it was way easier than he expected, and that other people whine too much. He had the same reaction to the Tough Mudder we ran last summer.
One of the things that he talked about a lot is how the Army recommends water, for pretty much anything that could be wrong with you. Headache? Sluggish? Muscles sore? Drink more water. He said that water was pretty much used as the cure for everything in boot camp.
I’ve been drinking a gallon a day for several months now, and I think the Army has it right. There is a huge difference in my mental acuity, coordination, and feeling of well being when I drink water, particularly if I start the moment I get out of bed. It wakes me up better than coffee. As a side benefit, I feel like I don’t have to worry about all of those studies that show that sitting constantly is bad for you, because you end up moving a lot more through the day to refill your water bottle and also to use the bathroom.
Drinking water also cuts down on cravings for sweet things- I think my mind associates sweet foods with fruits, which tend to be very liquidy. Drinking enough water helps cut down on these cravings. Try it out! Add more water to your diet.