I don't know (need city planners for this kind of stuff

)
However, it is the ambient temperature that would determine the influence of water vapor (the amount that would stay in the atmosphere)... close to entirely, as I understand it. I don't think we generate water in any larger amounts, except as a by product of energy generation. Water that would be absorbed by the soil would be added to the atmosphere (ie: off city roads), but the majority of that is run off into sewers, which tend to feed into oceans, negating the majority of the effect. The rest of the water tends to be consumed by humans, which also goes directly into the sewage system.
Having said that, this is just deductive - I don't know the actual numbers. Never heard it as an issue before.
edit: Just reading into it -
Greenhouse gas - Wikipedia, the free encyclopedia Seems like it really is just temperature that affects it... humans can't directly influence it easily.