North Americans are chronically dehydrated, but the problem is most acute in active individuals and athletes. The body needs 500 ml of liquid for each 500 gm of weight lost through activity, but athletes typically consume only half that. Even slight dehydration can compromise heart function and have a negative impact on cognitive function. As little as 1 percent dehydration (600 to 800 ml of water loss) can impair physical function, while 2 percent can reduce exercise capacity, and more than 7 percent can cause collapse.