You have to pick:

You are not allowed to urinate until the injection is complete (though you can immediately after).

I'll assume that all the water on Earth is turning into Coca-Cola, specifically.

First, all ocean life dies immediately.

There's 2.2g of dissolved carbon dioxide in a 335ml can of coke. So multiplying that out to the volume of water on Earth, 1,386,000,000 cubic kilometers, we get 9*10^18kg of carbon dioxide fizzing out into the atmosphere. Earth's atmosphere currently weighs 5*10^18kg so the atmospheric pressure goes up to 2.8 atmospheres and is 64% carbon dioxide. This kills all air-breathing life, probably in a matter of hours at most.

Carbon dioxide is, of course, a greenhouse gas. The amount that's been injected into the atmosphere here is unprecedented in Earth's history and will likely result in a runaway greenhouse effect. Earth's temperature will rise well above the boiling point of water and any remaining microbial life will die. Earth will become permanently sterile.

So... bad option. Don't take this one. :)

According to http://hypertextbook.com/facts/2001/DanielShaw.shtml 1 liter is at the very upper limit of the usual range of capacity for the human bladder, so most people aren't going to be able to hold that much and will risk rupture. Could be quite serious, and wouldn't be surprised if it'd lead to kidney damage and infection.