Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† hydrŏmantīa, ae, f., = ὑδρομαντεία, divination by water, hydromancy, Aug. Civ. Dei, 7, 35; Plin. 37, 11, 73, § 192; Isid. 8, 9, 13.