tried several time by reloading a game near a fountain with low health and a monster near me i had about 20 health i drank from fountain got acid monster attacked me i was still alive then i moved away from monster and died from acid
I died 2 rounds after drinking and it did not give me the achievement either. Possibly the achievement only fires if the intial "sip" kills you and not the subsequent acid burn effect...
THREAD NECROMANCY! Relevant thread searching is awesome. But yeah, I've tried it both ways now, getting killed with the initial sip of acid and getting killed by the subsequent acid burn effect and neither of those awarded the achievement. This is on the 1.08 Steam version, it still seems to be broken.
Beats me as to why, but on my third attempt at killing myself with acid fountain water, the achievement triggered. Not really sure why though, didn't do anything differently.