When controlling Kian for the first time and trying to find your way into the tower, you will come across the racist townie from earlier in the game preparing to start a bonfire with Crow in it. Behind the bonfire is a wine seller with a bird bath next to it. Nearby, on the other side of Crow's cage is a table with some beer casks and a dirty flagon. Get the flagon, fill it in the birdbath, look at it in your inventory, and use it to drink the water and unlock the achievement.