  We show that the universal properties of the rainfall phenomenon are the
scaling properties of the probability density function of inter-drop intervals
during quiescent periods, time intervals of sparse precipitation, and the
universal shape of the probability density function of drop diameters during
non-quiescent periods, time intervals of active precipitation. Our results
indicate that the continuous flux-like vision of rainfall based on quantities
such as the rain duration, rain intensity and drought duration is ineffective
in detecting the universality of the phenomenon. A comprehensive understanding
of rainfall behavior must rest on the acknowledgment of its discrete drop-like
nature.
