The speed that can be maintained is equal to a cost of ⅖ AP per combat hex. This equals a distance of 8.52 miles per hour, which can be maintained for a period of up to 3 hours.
For example, a 150 lb. character running in warm weather is losing 0.9 lbs. of water every hour, or 13.8 fluid ounces (1.72 cups, or 431 ml). This equals 2.3 fl. oz. per ten minutes, a little more than a quarter of a cup or 72 ml. This is about 4 swallows of water (which ranges from 16 to 20 ml per swallow). Running in this temperature is more or less feasible.
Of course, the runner can stop at any time and search for water. If the amount of necessary hydration is not achieved, however, movement while running is reduced to normal running speed (½ cost per combat hex) for the following ten minutes. After that, the runner must reduce their speed to a normal pace. Once the necessary amount of water has been imbibed to replace all that has been lost since the run began, the character may begin running again, until the three-hour limit has been reached.
See Running (athletic ability)