Besides storing drinking water, Castaic Lake is the lower reservoir in a pumped-storage hydroelectric system. During times of peak electricity demand, water is released from Pyramid Lake and run through the turbines at Castaic Power Plant. At night, when demand and electricity prices are lower, water is pumped from Castaic Lake to Pyramid Lake. The income from the electricity sold offsets a portion of the cost for pumping the water in some parts of the aqueduct, such as over the Tehachapi Mountains.