Water quality is crucial for both household and food industry. Many problems in drinking water distribution systems are microbial, including biofilm growth, microbial mediated corrosion and persistence of pathogens. Biofilms may be formed on variety of surfaces, in living tissues, indwelling medical devices, industrial or potable water piping system, or normal aquatic ecosystems. They are suspected of being the primary source of microorganisms in water distribution systems. In addition to health related importance, microbial growth in distribution systems can cause taste and odour problems, which can be contributed by the substances produced by some species of fungi. Understanding the effect of the environmental conditions on these fungi may help to improve distribution system management strategy. The nature and concentration of biodegradable compounds present in treated drinking water as well as the water temperature are some of the factors contributing to biofilm formation in potable water systems. In this study the effect of phosphorus concentration, temperature, light and darkness, on the biofilm forming potential of three fungal species were tested in the laboratory. A total of eight fungal strains of Trichoderma viride, Penicillium spinulosum and Aspergillus ustus were studied, of which all were previously isolated from Norwegian drinking water. Plate counts and relative luminescence unit (RLU) were used to analyse the biofilm colonization. The results from the present study indicated that all the fungal strains were able to form biofilm under all parameters used. Statistically significant differences were demonstrated for the effect of light and time on T. viride, and for the effect of temperature and time on both A. ustus and P. spinulosum. No variation between the different fungal strains within the same species was observed with respect to the investigated parameters. No effect of phosphorus on the biofilm formation potential of the three fungal species could be demonstrated.