This paper presents an environmental design that utilizes thermal storage and natural energy to meet the diverse performance requirements of an office building in Japan. The building could be made self-sustainable for a duration of three days by installing a well and a wastewater tank. Additionally, the air-conditioning system employed thermo active building systems (TABS) to eliminate uneven temperature distribution. The results indicated that a heat source system utilizing heat from well water could potentially reduce the annual energy consumption due to air-conditioning by 20%, thus suggesting a highly efficient use of medium-temperature water.