Water for City of Fresno customers comes from two primary sources – groundwater and surface water. For years, groundwater pumped up from an underground aquifer was the sole source of water for Fresno water customers. In 2004, treated surface water from the Surface Water Treatment Facility (SWTF) began augmenting the groundwater to create a more balanced water supply. To replace some of the water taken from the aquifer, rainfall and stream flow naturally percolate back into the aquifer. The City also runs an aggressive recharge program to supplement the natural replenishment of the aquifer.