Water poisoning sounds like an absurd way to go. Like oxygen poisoning which I think is also a thing.

@Helios_Five  
Holding it isn’t so much of an issue in the short term, you’re likely to piss yourself before you can do any serious damage unless there’s some kind of blockage or neurological issue. However Drinking an excessive amount of water in a short period of time will lead to water poisoning. How much really depends on the biology of the person and what they consume with the water. Now the fun thing is when we factor in equine anatomy. The average horse will drink 8-12 liters a day or about 1 gallon per 100 lbs. It’s hard to assume the size and weight of a pony, but she’ll probably out drink you. :p

@Helios_Five  
I’m pretty sure she’s counting on those restroom breaks for sure||~||. It’d also be a good time to get more snacks or water.  
Although I feel like Fiji would be the only one that would need to get up for that stuff. ( ͡° ͜ʖ ͡°)

Regarding the comment to picture Were some guy who died last year I think in a ‘see how much you can drink and hold it in’ competition.  
Turns out the body wants to get rid of toxic byproducts or something.
 
So I would recommend not taking her up on her offer if it refers to the picture in the comments.
 
Games though? Go ahead.

@Silent Wing  

 
Actually probably. But it is bottled and shipped by the case – nice and sealed. So that’s good!

<Fiji Water  
So some bottled tap water mixed with the sea breeze?

I like the implications of this :p