You should be drinking water every 2 hours when not exercising. During exercise you need to be topping up the fluid levels every 10-20 mins. During intense exercise it's important to develop a fixed drinking schedule: for every litre of water lost per hour you need to be drinking 2 pints of water, obviously spreading this out by drinking smaller amounts every 10-20 mins. The difficulty is knowing how much fluid you, as an individual, lose every hour; 1 litre of water weighs approximately 2 pounds and 1 pint of water weighs approx 1 pound. Next, we need to work out how much you should be consuming:
1) Make a note of the time just before you start training. 2) Write down your body weight in pounds (this should be nude weight, but as least clothing as possible will suffice) 3) Continue with your normal exercise routine, but keep a note of how much water you consume during this time. 4) Immediately after exercise strip down to a bare minimum and dry yourself off. weigh yourself again and make a note of body weight in pounds. 5) Make a note of the current time. 6) Calculate fluid lost by subtracting ending weight from beginning weight 7) Calculate exercise time by subtracting ending time from beginning time. 8) The amount of extra fluid you should be consuming, on top of the amount you previously recorded, should be 1 pint (16 ounces) for every pound lost during exercise. this should be consumed in 10-20 min increments.