San Diego's water is managed and regulated by a variety of entities, primarily subject to State and local laws and regulations. Water is allocated for residents, businesses, agriculture, and more. Desalination is being actively explored and developed. Here are some resources for you to consider during your Water Law research.
The San Diego Water Authority serves as San Diego County's regional water wholesaler. The Agency's mission is to provide a safe and reliable water supply to its 24 member agencies. The Water Authority is a public agency under the state County Water Authority Act Chapter 45.
A complete list of San Diego Water Authority member water and irrigation districts can be found here.
Here is a non-comprehensive listing of some major districts; others are readily found online or through their listing on the San Diego Water Authority site as noted above.
San Diego enjoys a western border on the gentle Pacific Ocean. So it's only natural that efforts are explored to desalinate water (that is, to remove salts from the water) for use on land.
The website for the Carlsbad Desal Plant in the North County is a great resource on this and related topics.
As well, the San Diego Water Authority is working with our neighbor to the South to explore sea water desalination in Rosarito Beach.
The San Diego Farm Bureau administers the San Diego Irrigated Lands Group, This organization assists farmers and others in implementing the myriad of water regulations that apply to our County. Their site is a wealth of information.