These AIO coolers typically have some kind of anti freeze in the coolant mixture.
I want to say the fluid in your AIO is mix of distilled water, Some sort of antifreeze (such as propylene glycol or some other sort of alcohol), and then trace amounts of anti-corrosives and biocides.
Methyl alcohol, ethyl alcohol, and propylene alcohol been used in the past as antifreeze in automotive coolant. Alcohol is the actual key antifreeze compound; the biocide compound is most likely benzalkonium chloride, copper sulfate, calcium sulfate or some other salt compound with a toxicity to bacterial and fungal life.
The Corsair H100i is a Asetek made cooler, most of Corsair, NZTX, Antec, and Thermaltake AIOs are by Asetek. All of those AIOs all have the same fluid.
The exact compound use in the AIO I am not sure of, and I don't want to take apart my AIO and buy test strips to figure out the exact formulation.
There is enough Alcohol in the AIO to allow it to ship reasonably safe during the winter months. But if someone wants to be cautious, you can wait till the AIO warms up to room temps before installation and just watch carefully for about 15-30 min for any leaks.