Water vapour has a short residence time in the atmosphere, is self-limiting (excess water precipitates out as rain or snow), and is already at equilibrium given ambient conditions.
The one variable that could drive additional water vapour is CO2, which by warming the atmosphere further increases the ability to hold water, and the amount of water vapour present.
If you want to reduce water vapour as a greenhouse-gas component of the atmosphere, reduce CO2 levels.
Just to be clear water vapor capacity increases due to temperature, for example, relative humidity measures how much water vapor is in the air for a given temperature. Any sort of increase in temperature will increase water vapor.
Yes, CO2 raises the temperature, you get a massive increase in water vapor, which again, is a more potent ghg. Reversing that same amount of CO2 does not magically reverse all of that water vapor. This is the crux of the problem, why water vapor is now also a problem that needs to be addressed.
The one variable that could drive additional water vapour is CO2, which by warming the atmosphere further increases the ability to hold water, and the amount of water vapour present.
If you want to reduce water vapour as a greenhouse-gas component of the atmosphere, reduce CO2 levels.
https://skepticalscience.com/water-vapor-greenhouse-gas.htm