When undiluted rum was served there was a test to prove the purity. If after soaking gunpowder in the rum, the powder still burned, the rum was considered to be uncut and, I guess, fit to be doled out.
Crewmen got a cup (normally a 1/2 pint) of grog a day, maybe more for holidays or before the gun smoke and splinters started. Officers and under aged seamen did not get rum/grog issued. Non-drinkers were given three pennies a day instead of the "tot". Royal Navy and East India Company ships were not tolerant of drunkenness in crew or officers. Not that such was all that rare as various "home brew" products were made, below decks, to augment the grog ration.