More than fours years time series of integrated precipitable water vapor (IPWV) derived from a regional GPS network is used to examine the climatology of IPWV in Hawaii. The long term average value of IPWV declines exponentially with height, but the dispersion or variability of IPWV declines linearly. During prevailing tradewind conditions, there is a correlation between the integrated precipitable water vapor at low elevation sites and the depth of the moist layer, as determined from radiosonde soundings. The relationship between IPWV and precipitation from automatic rain gages is investigated during tradewind conditions.