Thanks to Roger for providing a link to a DA calculator (couldn’t find a TAS calculator that considered moisture?). [;)]
Moisture doesn’t nearly have as much of an effect as pressure altitude or temperature on density altitude or TAS. That’s why your POH performance charts don’t incorporate water vapor content.
If you play with the calculator Roger pointed out, you might get the false impression that moisture can have a significant effect. Dew point varies less than does temperature. For example, you may wake up on a warm (upper 60s) and hazy morning with the dew point a juicy 65 degrees, but by the afternoon temperatures could easily hit the upper 90s. The dew point, however, may only find its way into the low 70s. When using such a calculator, make sure you take this into consideration.