Author Douglass Westfall discusses how Southern California gets its water and why this is important. Much of California’s water flows down from the Sierra Nevada Mountains, yet a large part comes from natural underground aquifers. These make up just part of the total water system that includes reservoirs, rivers, canals and pipelines. Fully, half of California's available water goes to agriculture, not people, as California grows more food than any other state. Yet this is only part of the story as California's population increases every ten years by some five million people, and California hasn't built any reservoirs for half a decade.