Experience of a novice in the use of commercial systems for computer assisted interpretation of mass spectra of compounds found in drinking water is presented. Recurring problems in GC/MS analysis of complex mixtures were analyzed by three computer systems: PBM, STIRS, and MSSS. Problems such as the presence of low level impurities, mixtures, quality assurance of reference spectra, and mass spectra which do not match reference spectra in the Registry of Mass Spectral Data are discussed. The performance of each system is discussed to aid the occassional or new user of these systems.