How much should you be drinking?
The old recommendation was that everyone should be getting of eight to ten cups (2.0 to 2.5L) of fluid a day. Unfortunately, this did not take into account the water we get from the food we eat and specifically excluded anything with alcohol or caffeine. This is a little outdated and the latest research shows the new formula is:
Men: bodyweight (lbs) x 9.176
Women: bodyweight (lbs) x 10.36
Thus a 135 lbs (61.5kg) woman should be drinking 1398.6mL, or about 1.4 L, of fluid a day.
Naturally if you exercise you should get a drink more to replace the water you lose through sweat. However, unless you exercise for hours in the hot sun, 500 to 750mL of additional fluid per hour of exercise is usually enough. This can come from all sorts of beverages, not just plain water. And it has recently been proven that, contrary to popular wisdom, caffeine is not a diuretic (making you go to the toilet more frequently) so you get as much hydration from plain tea and coffee as water.
What should you be drinking and when?
We drink during exercise for two reasons: To replenish water and electrolytes lost through sweating and to give us additional energy so we can keep working for harder or longer. Electrolyte drinks can be a great help before, during and after exercise as they replace not only fluids but also the essential salts lost through sweat and the glucose used by our bodies for energy.
How long your workout lasts, the temperature and the intensity of your workout all affect how much and what kind of beverage you need to drink. Common sense and your own body should be your guide, but here are a few general principles:
Workout Time: Less than 45 minutes
Drink: Water or Electrolyte tablets (or nothing)
Workout Time: 45 minutes to 1.5 hours
Workout Time: More than two hours
Workout Time: Race Day
Workout Time: Post-exercise