We present the design of a compact purge system designed for the TeraSmart terahertz spectrometer offered by Menlo Systems, but compatible with other spectrometers based on fiber coupled photoconductive antennas. While connected to the nitrogen (or dry air) source, the system effectively deals with water vapor absorption that is a well-known issue in terahertz spectroscopy limiting a signal-to-noise ratio. The system was designed for the lens-based version of the TeraSmart spectrometer arranged in a linear configuration for transmission measurements. However, the underlying idea can also be adapted to a reflection configuration or a mirror-based spectrometer with off-axis parabolic mirrors mounted in a cage system.