The same place that water came from on Earth... comet impacts and residual moisture from the impact that split the Earth-Moon system. Really the same place all planetary water and gas has come from.
There's not much left because it mostly boils off due to low pressure, but in dark crevasses it's likely to stay cold enough to remain condensed. It's been measured spectroscopically.
There's not much left because it mostly boils off due to low pressure, but in dark crevasses it's likely to stay cold enough to remain condensed. It's been measured spectroscopically.