Geostationary Operational Environmental Satellite (GOES) sounder-derived total column water vapor is compared with other data sources obtained during the 2002 International H2O Project (IHOP-2002) field experiment. Specifically, GPS-derived total integrated precipitable water (GPS-IPW) and radiosonde observations (raob) data are used to assess GOES bias and standard deviation. GPS integrated water calculated from signal delay closely matches raob data, both from special sondes launched for the IHOP-2002 exercise and routine National Weather Service (NWS) soundings. After examining the average differences between GPS and GOES product total precipitable water over the full diurnal cycle between 26 May and 15 June 2002, it was discovered that only 0000 UTC time differences were comparable to published comparisons. Differences at other times were larger and varied by a factor of 6, increasing from 0000 to 1800 UTC, and decreasing thereafter. Reasons for this behavior are explored to a limited degree but with no clear answers to explain the observations. It is concluded that a component of the GOES total precipitable water error (between sonde launches) might be missed when solely assessing the data against synoptic raobs.