A faucet with a slash through a drop — the international signage symbol meaning "don't drink this." Online it's mostly used literally (camping, hiking, disaster-relief posts warning about tap water) rather than as a joke emoji, since the pictogram is too niche to carry much metaphorical weight. It comes straight from the ISO 7001 public information symbol set, the same family that gave emoji its no-smoking and no-entry signs.
Keywords: dry, non-drinking, non-potable, prohibited, water