In this review, the reaction cycles based on redox reactions of alkali metals such as lithium, sodium, and potassium are systematically investigated as a potential water splitting technology operated at lower temperature than 500 °C. Assuming that all the cycles are operated in thermodynamic equilibrium condition, more than 1000 °C is theoretically required. Thus, equilibrium shift using phase transition of alkali metals is performed to decrease the reaction temperatures. The operating temperature of the lithium cycle is 800 °C because such high temperature is necessary to obtain high vapor pressure. The potassium cycle is potentially water splitting operated below 500 °C. However, strong corrosion is serious problem to develop it as practical application. Among them, the sodium cycle reveals the lowest operating temperature, which is 400 °C. Therefore, the sodium cycle should be categorized as one of the potential water splitting technology.