Its to do with a process called osmosis.lwm3398 said:Water... Poisoning? What is that and how does someone go about getting it?
Basically, water moves from an area of more water (concentration) to an area of less water, across the membranes of your cells, until they're roughly equal in water concentration.
When you drink water, it basically ends up in your blood, and when its at the right amount, your blood cells, and your tissue/muscle cells stay the right shape due to having enough water inside and outside the cells.
When you get dehydrated, imagine that there's "less" water in your blood, but it HAS to stay equal in amount on both sides, and so the water moves from the cell that it is in, into your blood stream (this includes blood cells). When there's not enough water in the cell, it collapses in on itself, like letting air out of a balloon.
The opposite is true for over hydration, water floods INTO your cells, from your blood, swelling them to the point of breaking (rupturing), like filling a water balloon with so much water it breaks.
To be honest, I don't see why they thought this would be a good competition in the first place, or at least have someone with medical experience on site first. 7.5 litres of water is a HUGE amount in one sitting, it takes common sense to realise water has to go somewhere, and if its not being peed?