Grog and working routines aboard sailing warships

Why could age-of-sail sailors drink grog and still perform skilled work?

It was a routine alternative when clean water was scarce, and experienced sailors were accustomed to the ration while remaining functional.

Alcohol was consumed partly because a ship could run short of clean water, making the alcoholic ration a safer routine drink. The ration belonged to the ship's provisioning system rather than existing only as recreation. Regular consumption also created tolerance, so sailors could remain competent after an amount that would affect an unaccustomed drinker. The practice joined the problem of water storage to the effects of a long-established daily routine.