X-ray diffraction patterns and stereoscopic microscope were used to analyze the scale and other mineral such as hydrozincite (Zn_5(CO_3)_2(OH)_6) and scholzlte (CaZn_2(P0_4)_2 · H_20). The scale In the water pipe consists mainly of Fe-oxide/hydroxide minerals such as magnetite, hematite, goethite and lepidocrocite and carbonate minerals such as calcite and aragonite. Calcite and aragonite are precipitated by the reaction of Ca and C0_2 in the water. Because water does not contain Fe, the scale results from the corrosion of water pipe. Zinc is able to eliminate the scale and protect the production of scale in the water pipe.