it's the foreshots, methanol, which in a rig like your would be the first 150 ml or so that attack the optic nerve. but i know, a shot of full strength neutral spirits will set you back on your heels.

when i was a kid, i knew an old man, and i mean born in the 1890s old, who lived in a shack in the swamp. all he ever drank (other than canadian club) was rainwater from a wooden cistern. we kids drank it too, and never got sick. it always had a bit of a green tinge to it. there are some of our brother distillers, i forget which forum, who only use rainwater in their mashes.