We showed in previous experiments that the melting temperature of hydrous pyrolite, at the transition boundary between wadsleyite and olivine, is abruptly reduced by the presence of 2 wt.% H2O. In this paper we determine the apparent solidus for CaO-MgO-Al2O3-SiO2-pyrolite with lower and geologically more reasonable H2O contents (0.5 wt.%). Phase relations and melt compositions have been determined at pressures of 13.5--17.0 GPa and temperatures of 1600 to 2100¿C. There was no abrupt decrease of solidus temperature along the phase boundary between olivine and wadsleyite in pyrolite with 0.5 wt.% H2O. However significant gradual decrease of the solidus temperature at pressures below 15--16 GPa still supports previous models for a hydrous origin of some ancient komatiites by dehydration melting of rising wet plumes at pressures of 4--10 GPa.