There is an overwhelming amount of evidence supporting the past existence of abundant flowing water on the martian surface, however the source for this water is less understood. Estimates of water in the deep martian interior from SNC meteorites yield low values (1–36 ppm H 2 O) that are incompatible with magmatic degassing as the primary source for this water. We have analyzed hydrous amphibole in the Chassigny martian meteorite, finding much higher water contents than previously reported. These values are consistent with a much wetter martian mantle (minimum range of 140–250 ppm H 2 O for the Chassigny source region), allowing for significant contributions of water to the martian surface by magmatic degassing. Furthermore, these results indicate the possibility of young (early–mid Amazonian), water-rich hydrothermal activity at the surface and subsurface, which could have been responsible for intermittent replenishment of water to these regions even after the onset of the cold dry climate that exists today.