Water service pipes made of galvanized steel were assessed by direct diagnosis according to major water basins, age of pipe, and their diameters. The tubercle growth and the hydraulic cross sectional area reduction rates from examination with the visual assessment showed that there was little difference among main water basins. However, comparing the results showed that their rates depended on the age of pipe indicating that as ages increase, their rates tend to decrease. Also, in the case of over 40 mm diameter, those rates tend to be higher than the case of less than 40 mm diameter. From the results of physical properties analysis, even though most of the sampled pipes satisfied Korea Standards (KS) of tensile strength and chemical composition, 90% of the sampled galvanized steel pipes could not satisfy KS of elongation. It could be thought that elongation was seriously effected by pipe deterioration in the view of physical properties and chemical compositions. In addition, the results of scale composition analysis revealed that the component ratio of Fe was highest, whose percentage was from 54.3 ∼ 69.8%, and then that of Zn was 0.09 ∼ 6.34%. In comparing corrosion rates on three water basins, the maximum corrosion rates of Nakdong-River basin was 0.064 mm/year (mmpy), higher than those of other basins. Also, the diameters of the sampled galvanized steel pipes increased the corrosion rates.