"Based on the mineral’s water content, the scientists estimated that the Martian mantle source from which the rocks were derived contained between 70 and 300 parts per million (ppm) water. For comparison, the upper mantle on Earth contains approximately 50-300 ppm water.
"'There has been substantial evidence for the presence of liquid water at the Martian surface for some time,' Hauri said. 'So it’s been puzzling why previous estimates for the planet’s interior have been so dry. This new research makes sense and suggests that volcanoes may have been the primary vehicle for getting water to the surface.'"Extensive Water in Mars' Interior (ScienceBlog.com).