With the summer heat scorching down upon most of us, two big issues are keeping cool and keeping hydrated. For those of us blessed by dry heat, it's easy not to feel as if you're sweating; the air soaks up your skin's moisture almost before it's shed. For those of us in humid environments, the air becomes hot and heavy, our sweat clinging to us like plastic wrap, making us feel consistently hot and wet. In either case, it's easy for us to forget to replenish those fluids we so rapidly shed.
Under normal circumstances, human adults are advised to drink 6-8 glasses of water per day. This is roughly the equivalent of 3-4 half-liter bottles of water, or two or three 700-ml sport bottles of water, or a two-liter bottle of diet soda. Depending on your personal health and which medical study you're reading, this may mean anything from "water -- and add another glass for each cup of caffeinated beverage you drink!" to "any beverage" to "all beverages, soups, and even the moisture naturally present in fresh fruits and vegetables". And depending on your personal health, that quantity may be a minimum, a maximum (for example, if you have certain types of kidney disease), or a guideline which should be adjusted for weather, activity, and the specific foods you are eating in a given day.
For most of us, it's a good idea to add additional water if we will be sweating a lot -- for example, if we are exercising or if it's very hot out. On my first trip to Las Vegas (for a computer-industry trade show and user-group conference), our hosts advised us to double what we would normally be drinking at that time of November back in the Northeast. The general rule of thumb I've been given for Renaissance faires is, "if you don't have the need to urinate at least once an hour, you're not drinking enough". The rule-of-thumb for hard exercise is to weigh one's self before, and after, one's workout, and to add back a glass of water for every half-pound one has lost. I've seen a couple of different suggestions for fluid management during endurance exercise, generally ranging from one-half to one liter of fluid per hour.
While I'm all for hydration, and while I do keep an active eye on how much I'm drinking during hot and/or active conditions, water intake is just one part of the picture.
Other factors include how quickly we process the fluids we drink, and what is -- or is not -- contained in those fluids. I'll talk about that a bit in my next post.
