The suitability of a broad focus tungsten tube was evaluated for total reflection X-ray fluorescence (TXRF) using a prototype TXRF unit based on the Vienna Atom Institute module. The detection limits obtained using a broad focus and a fine focus tube were studied for the determination of dissolved elements in rain water. The detection limits for the broad focus tungsten tube were three orders of magnitude worse than those obtained with optimized commercial systems, and ranged from 40 ng for S to 1.9 ng for Mn and somewhat higher at 5 ng for Ni. The use of a fine focus tube improved the detection limits by factors of 2–10 within the considered energy range. Precisions of about 15% and relative accuracies around 7% were obtained, for element concentrations far above the detection limits. A comparative study using TXRF, ion chromatography and atomic absorption spectroscopy showed a good agreement amongst the three techniques and indicated that elemental determinations in rain water could be confidently performed using a TXRF unit coupled to a broad focus tube.