Originally posted by robiles I do not care that much about f2.8. I am more interested in wr because in Germany it rains a lot, and when not, it is cloudy and humid.
The two best WR standard zoom choices for Pentax APS-C K-Mount are the DA* 16-50 and the DA 16-85. The DA 16-85 is a more recent offering, and as a result it's going to be harder to find good deals on that lens. But in terms of image quality, it's reputably very very close to the DA* 16-50, with longer zoom range and better flare control, but much slower in terms of aperture.
If either of those choices are too pricey, the next best WR choice is the DA 18-135.