During a game, which is going to be max intensity and varying heart rate, however usually a lot higher than 75%, this how much water you should drink: When you first wake up in the morning, drink around 250ml to replace any fluid lost from bodily functions overnight. 2 hours before sport, slowly drink 1 litre - don't chug it down all it once, you will feel bloated. Around half an hour before the game, sip down around another 250 ml.Just before the game, weigh yourself to get a baseline. During the high intensity sport, drink around 250 ml every 15 minutes. In some sports, this may be hard due to long gaps between breaks and limited subs. After the game, take your weight down again. For every Kg lost, drink around 250ml pf water over the half hour to hour.