Tonicity: Hypertonic, Hypotonic, and Isotonic Solutions.

The importance of tonicity and the tragic real life scenario mentioned in class:

Woman Dies After Water Contest. 

Court Settlement after water poisoning death

Below is a video link with the details of what happens during Water Poisoning.  It is based on the real  case of the "Hold Your Wee for a Wii" story.  This video explains in details what happens inside the body. It also explains how the condition can be treated.

Hold Your Wee for a WII

WATER INTOXICATION, ALSO KNOWN AS WATER POISONING, OVERHYDRATION, OR WATER TOXEMIA IS A POTENTIALLY FATAL DISTURBANCE IN BRAIN FUNCTIONS THAT RESULTS WHEN THE NORMAL BALANCE OF ELECTROLYTES IN THE BODY IS PUSHED OUTSIDE SAFE LIMITS BY EXCESSIVE WATER INTAKE.  

Endurance sports

Marathon runners are susceptible to water intoxication if they drink too much while running. This is caused when sodium levels drop below 135 μmol/L when athletes consume large amounts of fluid. This has been noted to be the result of the encouragement of excessive fluid replacement by various guidelines. This has largely been identified in marathon runners as a dilutional hyponatremia.^[5] A study conducted on participants of the 2002 Boston Marathon found that thirteen percent finished the race with hyponatremia. The study concluded that the strongest predictor of hyponatremia ( low sodium levels in the blood) was weight gain while racing (over-hydration), and hyponatremia was just as likely to occur in runners who chose sports drinks as those who chose water.^[5] Medical personnel at marathon events are trained to suspect water intoxication immediately when runners collapse or show signs of confusion.

The information above explaining water intoxication was copied from Wikipedia.