A method for determining the dependence of the dielectric permittivity of municipal refuse on its volumetric water content is developed and tested. The method is based on time domain transmission (TDT) measurements collected with an automated network analyzer (ANA). Measurements in variably saturated sand were first made to test the method's ability to measure the apparent dielectric permittivity. The method was then extended to samples of municipal refuse to determine whether a single calibration can be used to describe the relationship between the dielectric permittivity and the volumetric water content of refuse. The results show that the relationship between the dielectric permittivity and the volumetric water content within the refuse shows significant spatial variability. The results do show, however, that a calibration based on multiple samples collected throughout the landfill can be used to measure the volumetric water content with a root mean square volumetric water content measurement error of <0.04 cm3 cm−3. Deviations from the common calibration are not explained by variations in bulk density or porosity among samples. It is recommended that a calibration be derived from samples collected throughout a municipal landfill before a water content monitoring method based on dielectric permittivity measurements is used.