Biotransformation enzyme that catalyzes the hydrolysis of arene and aliphatic epoxides to less reactive and more water soluble dihydrodiols by the trans addition of water (By similarity). Plays a role in the metabolism of endogenous lipids such as epoxide-containing fatty acids (PubMed:22798687). Metabolizes the abundant endocannabinoid 2-arachidonoylglycerol (2-AG) to free arachidonic acid (AA) and glycerol (PubMed:24958911). cis-stilbene oxide + H2O = (1R,2R)-hydrobenzoin 1-(4-methoxyphenyl)-N-methyl-N-[(3-methyloxetan-3-yl)methyl]methanamine + H2O = 2-{[(4-methoxybenzyl)(methyl)amino]methyl}-2-methylpropane-1,3-diol 8,9-epoxy-(5Z,11Z,14Z)-eicosatrienoate + H2O = 8,9-dihydroxy-(5Z,11Z,14Z)-eicosatrienoate 11,12-epoxy-(5Z,8Z,14Z)-eicosatrienoate + H2O = 11,12-dihydroxy-(5Z,8Z,14Z)-eicosatrienoate 2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-glycerol + H2O = (5Z,8Z,11Z,14Z)-eicosatetraenoate + glycerol + H(+) Inhibited by 10-hydroxystearamide and methoxy-arachidonyl fluorophosphate. Found in liver. In some populations, the high activity haplotype tyr113/his139 is overrepresented among women suffering from pregnancy-induced hypertension (pre-eclampsia) when compared with healthy controls. Variations in EPHX1 gene non-coding regions have been observed in a patient with hypercholanemia. The pathogenicity of these variants has not been confirmed. Belongs to the peptidase S33 family.