I don't believe I was making any claim beyond what was discussed at the press release. They seemed to claim that the methane was destroyed within 4 years and possibly within one year. It used to be thought that methane had a half life of around 300 years on Mars, so a mechanism is needed to destroy it in short order to explain why the local concentrations do not spread out more over time. The most likely method suggested at the meeting was oxidation, perhaps via hydrogen peroxide on dust grains that can circulate from the upper atmosphere.

I am merely asking the obvious follow-up question: if methane is oxidised, then what happened to the water from the oxidation in those zones where water spectra did not overlap the methane signal? Where the signals overlap, one could say the water signal was possibly sourced by oxidation rather than be independently sourced. Of course, the water signal still could be independent. But the real puzzle is the absence of a water signal at the presumed site of methane destruction in the dry zones if natural oxidation is the mechanism. How does the water hide in one place but not the other?