The presence of compact obscured nuclei in luminous infrared galaxies (LIRGs) is very well probed by the detection of highly excited absorption lines of OH and H2O in the far-infrared (far-IR), which require warm and optically thick dust to pump the high-lying rotational levels. We are using a spherically symmetric radiative transfer code to model the H2O lines, OH lines and continuum from these objects. We discuss the results and analysis of Herschel observations of the compact obscured nucleus in the extremely H2O luminous LIRG Zw 049.057. In this galaxy we have found very high H2O abundances in a Compton thick compact core. Abundant 18O bearing species also suggest the presence of a relatively young starburst. We compare this to our observations and modeling of the luminous merger component Arp 299a, which is another source with prominent H2O and OH lines. Our preliminary results, however, suggest that its nuclear activity is in a different evolutionary state compared to Zw 049.057.
