California's interconnected water system serves almost 40 million people and irrigates over 5,680,000 acres (2,300,000 ha) of farmland. As the world's largest, most productive, and potentially most controversial water system, it manages over 40 million acre-feet (49 km3) of water per year. Use of available water averages 50% environmental, 40% agricultural and 10% urban, though this varies considerably by region and between wet and dry years. In wet years, "environmental" water averages 61%, while in dry years it averages 41%, and can be even lower in critically dry years.

Agriculture is a significant sector in California's economy, producing nearly US$50 billion in revenue in 2018. There are more than 400 commodity crops grown across California, including a significant portion of all fruits, vegetables, and nuts in the United States. In 2017, there were 77,100 unique farms and ranches in the state, operating across 25.3 million acres of land. The average farm size was 328 acres (133 ha), significantly less than the average farm size in the U.S. of 444 acres (180 ha).