This study presents the relationships between ion concentrations and sources of ions in the precipitation events which happened on a) September the 08th, 2007 b) November the 10th, 2007 and c) December the 05th, 2007. Fortyfour sequential rain samples were collected in three rain events that were sampled in Istanbul-Turkey making use of a sequential rain sampler. Concentration of the main cations (K+, Ca2+, Na+, and Mg2+) and main anions (Cl-, SO42-, and NO3-) were analyzed. The ratio of the mean Ca2+ (0.85) non-sea salt concentration to the mean total concentration led to the conclusion that most of the Ca2+ came from soil. This ratio for SO42- ranged between 0.49 and 0.98, indicates a possible conclusion that the domestic heating and industrial activities were the main source of this ion.