Grog was watered rum, mixed at a 3:1 ratio (three parts water to 1 rum). As punishment, some Royal Navy captains served "six water" grog, which was the sailor's ration mixed with six parts of water.

hi! there was a post asking about grog a few weeks ago, so you can get started here:

It's National Rum Day! My question is, why is rum often associated with pirates? And what is grog?

and that post links to this one for more info

How large were the daily rations of alcohol in various historic armed forces and how did their consumption affect soldier's performances and health?