Sodium trichloromethanesulfonate monohydrate, Na+.CCl3SO3-.H2O, crystallizes in P2(1)/a with all the atoms located in general positions. The trichloromethanesulfonate (trichlate) anion consists of pyramidal SO3 and CCl3 groups connected via an S-C bond in a staggered conformation with approximate C3v symmetry. The water molecule is hydrogen bonded to the sulfonate O atoms, with one water H atom forming weak bifurcated O-H...O hydrogen bonds to two different trichlate ions. Two water O atoms and three O atoms from different SO3 groups form a square-pyramidal arrangement around the sodium ion.