During the time over which the data for a regional hydrogeochemical survey are collected, the physical and chemical attributes of the ground-water flow regime may exhibit appreciable temporal variation. A case study is presented in which the temporal variance of many physical and chemical attributes of ground water at single locations was close to or even exceeded the spatial variance of concentrations measured over the region at a single point in time. Thus, the results of a multivariate analysis of the spatial variability could have led to incorrect inferences had the regional sampling not been done within a period of time that was short enough so that no appreciable temporal variation occurred. A methodology using both spectral and multivariate analyses was used in determining: (a) the window of time allowable in collecting the water samples so that the temporal variability of the attributes did not affect the spatial analyses, and (b) the dominant factors that explain the spatial variability of physical and chemical attributes at that particular period in time.