Typical tank designs have relied on water inflow and outflow for mixing. Reliance on this passive mixing has been revealed to be ineffective in most cases. Water quality deteriorates when thermal stratification occurs in the upper part of the tank. Cooler fresh water enters the bottom of the tank and fails to mix with the warmer water in the upper region. The cooler fresh water is the first to exit the tank, leaving the warmer unmixed water. A properly designed mixing system will help eliminate thermal stratification and dead zones. In addition, mixing systems can be designed with aeration which has been shown effective in reducing trihalomethanes (THM).