Summary
Water vapor is a byproduct created by combustion of fossil fuels. Every day, humanity releases 8 billion kg of water vapor into the atmosphere from combustion. However, this is just a small fraction of the 900 trillion kg of water naturally evaporated into the atmosphere each day. While it is possible that production of water vapor can alter humidity (and as a result, temperature, evaporation, cloud formation, and precipitation), as well as global sea levels, the amount created by combustion is trivial compared to natural evaporative processes.
The one exception is water vapor released in the high atmosphere by aircraft where it forms contrails and cirrus clouds. There is some evidence that this may cause local warming and possibly global warming.
The good news is that you and I can continue burning fossil fuels without worrying about the consequences of creating 8 billion kg of water vapor per day. The bad news is that fossil fuels also create of 16 billion kg of carbon dioxide and trillions of aerosols (particles) per day. And the severity of their impacts on climate and weather are much more concerning. But we'll leave those topics for some of the other websites out there. Here's some links to a few of them in case you're interested. I hope you enjoyed learning about water vapor as a combustion byproduct!
2001 IPCC Climate Change Report:
http://www.ipcc.ch/pub/un/syreng/spm.pdf
Intergovernmental Panel on Climate Change website: http://www.ipcc.ch/
The Greenhouse Effect: http://en.wikipedia.org/wiki/Greenhouse_effect
All about Aerosols: http://earthobservatory.nasa.gov/Library/Aerosols/