The NASA Water Vapor Project (NVAP) has been creating a daily water vapor dataset spanning 1987-2010. One device used to collect the total precipitable water (TPW) data is the Special Sensor Microwave/Imager (SSM/I). The SSM/I is most accurate when collecting TPW data over oceans. Land contamination is a large source of error when using SSM/I so a landmask is used to run data through to filter the land out. Therefore, it is critical to test the accuracy of the SSM/I. Global Positioning System (GPS) is being used to interpret the more globally available SSM/I satellites. Data from three SSM/I satellites (F13, F14, and F15) and GPS receivers from January 2003 were used in this analysis. The SSM/I data was matched to GPS stations based on location and the time the data was collected. This ensured that the TPW data being compared was from the same time and place. The GPS TPW was plotted against the SSM/I TPW to analyze the accuracy of the SSM/I readings. Then GPS island stations were isolated with a landmask and used as a source of SSM/I comparison as well. The relationship between the GPS and SSM/I data was found to be linear with some scatter. SSM/I F15 has a greater problem with scatter and most of the problem stations were found to be in Japan. A better understanding of water vapor will help with creating more accurate hydrological, weather and climate models in the future.