what will water vapor affect?

Answer 1

Depends on what and where and how much? Vapor from a vaporizer needs to be away from wooden furniture, walls and anything that water wouldn't need to be around, same with a humidifier, no wood, walls, pictures or anything water shouldn't be around...if it's warm or hot, even worse.
Also, it will affect the humidity and moisture in the area.

Answer 2

The biggest effect water vapour will have is on climate. Water vapour is capable of assisting the greenhouse effect by trapping the heat from the sun. If the temp on earth continues to rise the ocean temp will rise also and so the amount of water vapour going into the atmosphere will increase.

It could become what is known as a runaway greenhouse effect with more and more water vapour trapping the suns heat and therefore releasing more and more water vapour.