WormWood Ring (5e Equipment)
From D&D Wiki
A ring made out of a shard of Wormwood. The ring has a wooden appearance but is made of a strange metal. The ring is jet black and oily feeling. Any water or liquid touched by this ring becomes poisoned and anyone who drinks the water takes 1d4 poison damage every hour and is poisoned until the water they drank is excreted from their body.