The growth of Ce:(Lu1-xYx)2SiO5 single crystals by the hydrothermal technique is demonstrated. Crystallographic defects are suppressed thanks to the growth at much lower temperatures, and therefore, the complete incorporation of cerium in the Ce3+ valence state is obtained. The growth under supercritical water lowers the temperature to less than half of the melting point. In contrast, crystals grown from melt by the standard Czochralski technique possess intrinsic defects and undesirable Ce4+ ions as charge compensators. The growth of large-size single crystals with improved scintillation properties at a low cost is envisaged.