NHC-Au-X (NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, X– = BArF–, BF4–, SbF6–, OTf–, NTf2–, ClO4–, OTs–, TFA–) catalysts were tested in the hydration of alkynes. A complete rationalization of the counterion effect enabled us to develop a highly efficient methodology under solvent-, silver-, and acid-free conditions. Thus, it was possible to use room or mild (60 °C) temperature and to reduce the catalyst loading up to 0.01 mol % with respect to the substrate, leading to high TON (104) and TOF (103 h–1) values. The favorable catalytic conditions allowed us to reach very low E factor (0.03–0.06) and high EMY (94–97) values. Finally, the absence of solvent permits easy separation of the liquid product from solid catalyst and ionic additives by distillation, giving products with high purity that are uncontaminated by metals. This opens the way to catalyst recycling (up to four times) without loss of activity. The overall catalytic and kinetic evidence, supported by computational results, confirms t...