This is covering ground touched on in previous CP’s, but it EASILY merits reiteration and elaboration.  Dehydration sucks.  An old teacher of mine put this simply, and only had to say it once.  Lack of water will drop you faster than many other passive needs, excepting lack of air, so it bears paying attention to.  Habitually carrying a water bottle is not a bad habit to be in, as has been mentioned in previous articles, whether it’s a soft drink bottle you just kept using (they’re durable enough), or a fancy steel / aluminum / lexan one that could potentially fall off a cliff with little ill effect.  (Keep in mind a good strong bottle can also make an admirable clubbing tool, if you really need.  Hit with the corners, if you have a choice, the sides tend to cave in with abuse.)  In hotter conditions, as you loose water through sweating, you will need to do more than just re – hydrate, you may also need to put more salt / sugar in your system, since they are also lost when you’re sweating.  Sports drinks (Gatorade), are the obvious taste appealing solution, and come in powdered form which is easy to use as you need.  Mixing them about half the recommended strength works well.  If it’s not available, small amounts of pickle juice, table salt, or even sea water can substitute.  Use any with care, ESPECIALLY with the sea water, since getting too much salt in your system will only make the dehydration worse, and ocean water has a tremendously high salt content.  (A few cups can take you from thirsty to dangerously / fatally dehydrated FAST.) 

Good luck and drink up!