Naturally, daily fluid requirements will vary with environmental conditions, clothing and exercise intensity and duration.

Even mild dehydration-1 per cent of body-which would represent approximately.75 to 1 litre of water (1 per cent of 75 Kg = 750 ml.) can create a reduction in muscle performance and start to show dehydration symptoms. Early symptoms are headaches, dry eyes (ask any contact lens wearer what happens after a couple of glasses of wine), drowsiness, loss of concentration, irritability. If the dehydration is 2-3 percent, serious performance inhibition occurs. Dr. David costill demonstarted that at these low levels of dehydration 1-3 percent even the time for 1500 metres was inhibited. The time for a competitive 10 K was reduced by 2.5 minutes which is serious in a 30 min 10 K. Muscle cramps are also a sign of inadequate fluid replacement and electrolyte loss, particularly calcium and magnesium. Even "Lactate threshold"-an indicator of maximal work performance ability is lowered which is not a good thing in high intensity, endurance competition. Thicker blood, fast heart rate, negative changes in blood pressure are other symptoms.

Don't wait until you are thirsty to decide to drink. Fluid replacement is part of a daily plan. Thirst is a sign-too late-of dehydration, performance is already impaired.

You actually lose significant fluid just sitting in an air conditioned car or office. Frequent drinks of water during a long automobile trip will reduce apparent road fatigue. The same applies to sitting at your desk. A friend has a water bottle holder mounted on the dash of car to encourage convenient hydration while driving.

Here, are typical water losses during exercise: 1 hour of weight training = 227 gm; 45 minutes of swimming = 283.75 gm, a softball game = 454 gm; 5 mile run = 681 gm, 45 minutes of full court basketball = 681 gm, bicycling for 1 hour = 936.37 gm. and a marathon = 3291.5 gm.

As the environmental temperature, exercise intensity and or duration increases, you need to drink more and may want to switch to a quality sport drink (one made with a glucose polymer like maltodextrin rather than table sugar and 6-8 electrolytes rather than just sodium and potassium) to avoid a condition known as Hyponatremia or water intoxication caused by electrolyte loss and excess water intake. During the famous Daedalus man powered flight over the Aegean Sea (energy equivalent of 3 non-stop marathons) in 1988, the athlete lost only 1.5 Kg and had normal blood chemistry at the end. He drank a cup of high quality sport drink every 15 minutes for just over 4 hours. Cool beverages are absorbed better than room temperature or warm beverages.