As time continues in the canyon, what does Ralston's water supply mean to him?

More than just physiological survival, it becomes a psychological measure of the time he has left to live. As he sees his supplies dwindle, he feels he is closer to his death. Though he saves his urine, he still does not yet know whether it works considering its color and thickness. When Ralston loses half his water supply due to an accidental spill, he realizes how much the water means to him. Instead of a sand clock, he lifetime is now measured by his water bottle.