A highly efficient hydroxylation of (hetero)aryl halides using water as a hydroxyl source via Ni catalysis promoted by PhSiH3 under thermal catalysis is reported. This methodology provides a general procedure to obtain diverse multifunctional pharmaceutically phenols and polyphenols, some of which are proven challenging to be synthesized using literature methods. Mechanism studies demonstrated that the addition of PhSiH3 led to the generation of active Ni(I) species, which catalyze the hydroxylation via a Ni(I)-Ni(III) pathway.