Water ice deposits at the lunar poles could be a crucial source of water required to sustain human presence on the lunar surface. Microwave heating could be used to extract this water. Recent work has shown that microwaves efficiently heat lunar simulants, and numerical simulations have shown that this is equally applicable for the actual lunar regolith. Icy simulants can be heated efficiently where extraction of large amounts of water has been shown, but work to date has been limited in the sample temperatures possible. In this work, lunar simulants doped with various water contents were chilled to temperatures of 115 K and heated in a microwave heating unit (MHU). The MHU supplies microwaves, adjustable in power from 0 to 1 kW, to samples in a cavity capable of operating at pressures down to 10^-5 mbar. The mass loss of water was recorded and compared to the original water content to calculate the extraction efficiency (EE) of the process, which was found to be higher for samples with higher water contents.