In the Lighthouse, Thomas Wake offers a drink to Thomas Howard:
Thomas Wake: Still tastes o'the head? Ah, find some chirk in ye, lad. Now is the time for gab and chatter.
What does "Still tastes o'the head" mean?
Head is naval and boating slang for a toilet or bathroom. It derives from the days that the toilet was placed at the bow of the ship.
"Young" is still drinking water at this stage of the movie, and the cistern on the lighthouse has been contaminated:
YOUNG, cigarette in his mouth, opens the hatch of a porridged brick water tank: It lets out a putrid stench that knocks YOUNG’S face back a few inches. He tosses away the cigarette and covers his mouth and nose with the handkerchief around his neck. He looks inside: It’s full of mold and frothy sludge. It’s what he’s been drinking
"Old" is asking whether the water still tastes like its from a toilet, and wouldn't he prefer some liquor.