First, there was the initial settlement, spurred by the gold rush of the mid 1800 's. During this time miners, ranchers, farmers, and manufacturers flooded the area to claim the wealth they had heard of. Laws to be followed, which applied to water, was prior appropriation, or "first in time, first to right." Water users acquire ownership of water simply by taking it from a water source and putting it to use, as long as it was beneficial. Prior appropriation also meant that in times of drought, or low stream flows, the oldest water rights must be satisfied before a juniors rights. Water users were allowed to trade their rights of use with others.
By the 1900 's, settler 's who came for gold, and had failed began farming. But the success of agriculture is dependant on surplus of water. This triggered a new demand for irrigation. Public and private companies irrigated the land to fulfill the need.
Later it was recognized that previous generations were not focusing on developing new water supplies. They only were focusing on existing water supplies which became a concern for environmental protection. Since this recognition, new policies and procedures were put into place. An example of this would be the Clean Water Act, which limits the construction of new water projects, and has curbed the water appropriation rights. In 1994, the Bay Delta Accord was signed under the influence of the Clinton administration. The Bay Delta Accord created CALFED, a federal-state task force who 's goals are to develop long term plans to improve the ecological health of the Bay Delta System. The Delta is the nation 's largest estuary system providing 2/3rds of the states drinking water, irrigates more than 7 million acres of farmland, and is home to more than 750 plant and animal species.
References: http://www.pacificresearch.org/pub/enviro/watermkts/html Gleik,Peter,"Capitol Hill Hearing Testimony, California water management". May, 20, 1999.