[chris_va]

It's a reasonable question. While I am not a climatologist...

Anthropogenic evaporation is probably minuscule next to deviations in natural evaporation due to small changes in temperature. A single hurricane, for example, dumps more power (as heat) than all human power generation.

Also, unlike CO2, I would also guess that atmospheric water probably reaches equilibrium much faster (half life ~1 year instead of ~30 years).

[dnautics]

There is basically no equilibrium condition here. If you mean that there is a more 'inelastic' equilibrium constant, then keep in mind that the concentration level governed by such a constant is dependent on rate in versus rate out, and there are certainly ongoing inputs of ag water. We've completely drained several seas and underground aquifers as a result of human activity in the last 50 years.

[chris_va]

The amount of water used globally (approx 10^13 m^3) is only about 2.5% the total yearly evaporation off of the ocean (approx 4*10^14 m^3).

I suspect small changes in climate have a much greater effect on net evaporation.