The runoff time series play an important role in such activities of water management as planning, designing and operation but is not sufficiently monitored in terms of observed timing length and geographical locations. The rainfall-runoff models, of which models of conceptual types, represent effective tools for overcoming this difficulty. However, the efficiency of using modeling as a tool depends on whether the users understand characteristics as well as the domain of application of models. This paper deals with main limitations of conceptual rainfall-runoff models to avoid the situation where they are incautiously applied and as a result do not help to meet the research objectives.