The Clinical Journal of Sport Medicine wrote an article, (Preventing Deaths Due to Exercise-Associated Hyponatremia: The 2015 Consensus Guidelines), about the dangers of hyponatremia while exercising.  Hyponatremia is the condition of hydrating in such excessive amounts that the level of sodium in the blood becomes too low.  When this happens it causes harmful effects to the body, and in severe cases death.  Over hydration causes this because primarily through urination, and perspiration, sodium gets excreted from your body.

There is strong evidence showing that aggressive hydration is harmful to athletes.  Even so, coaches and athletes still somehow have the mindset of: "hyperhydration has health and performance benefits, while exercise-associated hyponatremia is rare."  In 2014 two cases of football players dying due to hyponatremic encephalopathy were reported; the commonality was excessive fluid consumption.

"These are deaths in young healthy people in the “prime” of their life, and most importantly, they are 100% preventable. How can anyone overstate the significance of a death in a healthy athlete who had the promise of their future cut short, especially when it was avoidable?"

There is no evidence that supports the mass consumption of liquids prior to or during exercise.  There are easy to follow hydration principles that lead to safe consumptions of liquids prior to and during activity that prevent exercise-associated hyponatremia.  One is to drink only when you are thirsty.  This is based off of our body's natural regulatory ability.  The other technique is to estimate hourly sweat loss.  Do not drink more than you will sweat.

To give perspective of how much is too much, the article gave an example of a collegiate athlete.  This athlete developed hyponatremia after receiving 5 liters of intravenous fluids, combined with drinking 3 liters of sports drinks, all within 5 hours.

I personally am always aware of how hydrated I am, and am therefore a little paranoid to try the "drink only when thirsty" approach.  The fact of the matter is, do not drink absurd amounts of liquids ever, especially prior to or during exercise!  If you are in taking liquid to a point where you are physically uncomfortable, that is too much.