Your body is like an engine, and it requires fluids to keep it cool, lubricated, and performing well. It doesn’t matter what you are doing, you need water, lots of it. It is essential that you keep yourself well hydrated before, during and after each and every activity if you want to maintain good performance. Good hydration will also help to avoid early fatigue during outdoor activities.
Even slight dehydration can produce a serious downturn in performance through an increase in body temperature. Your body needs adequate fluid stores to produce sweat that evaporates and cools the body, and to keep your vital organs functioning properly. As a quick rule of thumb, expect to consume at least 16oz of water per hour more in very hot weather or if you are big person. In addition to drinking frequently during any outdoor activity, you should drink plenty of fluid before any extended outdoor activity. Unless you haven’t been working too hard or been outside for too long, you should plan on drinking at least 16oz as soon as possible to replace any sweat loss.
As your body will still be producing sweat and also urine you actually need to replace one and a half times the volume of sweat that you have lost. You can check this by weighing yourself before and after your activity. For example, if lose two pounds during your activity, this means you have lost about one quart of sweat that you have not replenished (each quart of sweat weighs about two pounds) and you actually need to drink 1 1/2 quarts of fluid to rehydrate fully.
If you have lost a lot of sweat, it is important that you have a drink that contains some salt (sodium) to help to rehydrate the body. You will continue to feel thirsty until you are completely rehydrated. Plain water, however, can actually switch off the thirst mechanism; but having the presence of sodium in the water prevents this. It’s not essential to worry about the other minerals and electrolytes that are contained in commercial sports drinks. Although they are lost in sweat, there is not an immediate need for them unless you are out in more extreme (hot) environments. In which case an electrolyte drink with minerals is a good idea.
Drink before you feel thirsty. Let me say that again, do not wait until you feel thirsty before drinking as thirst is a poor indicator of the need for fluids. A feeling of thirst usually means you’ve waited too long and you’re already dehydrated. Signs of dehydration include headaches and fatigue. Keep yourself hydrated by drinking small, frequent amounts of fluid during any outdoor activity (two or three gulps’ every 10-15 minutes) even when you are not thirsty. You’ll still be generating heat, and perhaps sweat, and losing moisture from your body through your breath. Your body can usually process between 28 and 32 ounces of fluid every hour, so you should drink same amount every hour. Unfortunately, you’re unlikely to want to drink 32 ounces per hour which is why you’ll need to drink before and after.