It is frequently assumed that one methane molecule produces two water molecules. Applying various modeling concepts, we find that the yield of water from methane is vertically not constantly 2. In the upper stratosphere and lower mesosphere, transport of intermediate H₂ molecules even led to a yield greater than 2. We conclude that for a realistic chemical source of stratospheric water vapor, one must also take other sources (H₂), intermediates and the chemical removal of water into account.