This work focuses on the modeling and simulation of a mixing system for domestic use, which includes the water saving function. Water to be saved is the cold or partially cold water that reaches the mixing valve through the hot water inlet, as the tube length between the hot water source and the mixing valve is initially filled with cold water. Water saving function is obtained through a storage tank for accumulation of the initially cold or partially cold water, which is later used to feed the cold water inlet of the mixing valve. The accumulation system is designed such that accumulated water is preferably used than the cold water coming from the main cold water supply/distribution system to feed the cold water inlet of the mixing valve. Modeling considers fluid flow through the internal chambers of the system, the pressure evolution of water when flowing through the internal chambers of the system, and the temperature evolution of the separated and mixed water flows along the system. Simulation of the overall system is made using specialized tools to deal with stiff equations’ systems. Results show that, under real conditions, potable water savings of nearly 80% can be obtained relative to the water that is usually lost.