In my college nutrition courses I studied all sorts of entirely impractical strategies for hydration. One of these was for outdoor physical activity: 90 minutes before exercise have 16 ounces of water, then during exercise have 8 ounces every 15 minutes. Finally, note the difference in your bodyweight over the course of your activity (using the scale you keep in your backpack, I guess) and drink 20 ounces of water per pound of bodyweight lost. While I know this has value for professional athletes, this is just too much of a pain to be worth it for everyone else.
These are the simple keys to practical hydration:
1. Start with about half your body weight in ounces. (So, if you weigh 150 pounds, then try about 80 ounces of water — most water bottles are about 20 ounces, so finish four of them today.)
2. Check your urine. You should be able to read through it. If it is dark, then you need more water.
3. You should sweat during exercise. If you exercise with some actual intensity and you don’t sweat, I’d guess you’re pretty dehydrated and that you could get so much more out of your body (and feel better in the process) if you followed the advice above.
4. You should not gain weight over the course of exercise. If you are one of the few people who thinks they might drink too much water (it does happen), then go through the trouble of weighing yourself before and after exercise. If you gain a pound or more during exercise, then that is probably too much. Back off because there is too much of a good thing.
The bottom line is that you can either sip water every five minutes or gulp your water once an hour during your workout or hike. If it’s the same amount of water you’ll get about the same result provided you are hydrated on a day to day basis.