The water tanks are widely used for the safe storage of potable water, which are installed on either the basement or the top floor inside of the buildings. Therefore, the water tank systems assembled with many unit panels are generally adopted and the rectangular plan water tanks are most popular. To resist the water pressure acting on the side walls of tanks the internally reinforced system using metal tie-bars has been most commonly used. However, many problems related to the lattice internal reinforcement system require the development of the externally reinforced water tank, which does not have any latticed tie bars inside the tank. In this study two different systems have been developed using the external steel frames with either the SMC water tank panels or the PosMAC(coated steel) water tank panels. The experimental tests have been performed under the static hydraulic loadings as well as the seismic loadings through the shaking table test.