About 80% of our water supply comes from groundwater that is pumped by local wells we own. These wells are located in the San Gabriel Valley and Central Basins.

The Basins are giant underground reservoirs that can cover hundreds of square miles. Water is collected in these basins when rainfall or water runoff seeps into the aquifer, an underground area of rock, clay, sand and gravel that stores the water. The Main San Gabriel Basin is 167 square miles and contains an estimated 8.6 million acre-feet of water. The Central Basin is 278 square miles with a capacity to store 13 million acre-feet of water.

Suburban obtains its remaining supply from surface water (which comes from lakes, rivers and streams). The Metropolitan Water District of Southern California, which imports water via aqueducts from Northern California and the Colorado River, is our largest provider of surface water. In addition, we receive surface water from Covina Irrigating Company.

Although groundwater and surface water are both excellent sources of supply, groundwater usually requires less treatment than surface water. Because groundwater is pumped from deep within the earth, it is generally free of contamination from bacteriological sources and therefore only chlorine is used to disinfect the water. Surface water, however, requires a more extensive treatment process. Before surface water is distributed to customers, it must be filtered and disinfected with chlorine and/or chloramines at treatment plants to control bacteria.

Some Suburban customers may receive either groundwater or surface water exclusively, while others may receive a blend of both depending upon where they live or according to availability. If you would like specific information as to your source of water, contact our water quality department at (626) 543-2500.