Newly approved by the voters, Proposition 64 (AUMA) potentially sets the stage for even more mass cultivation of cannabis in the state of California than we currently have for medical marijuana. A crucial provision in AUMA (now codified in Bus & Prof Code §26056(c)) requires that all applicants for a license to grow the plant must not only demonstrate to the permitting authority that the prospective cultivator has a source of water to grow the plant but also submit certification that the cultivator has legitimate water rights “under state law.“ This will not be an easy hurdle to overcome in our drought-driven state. California water rights in general have been in jeopardy since 2011, because of the shortage of both rainfall and groundwater. Water supply and water quality were already critical issues in the cultivation of medical marijuana. So is there enough water in California to support the cultivation of recreational cannabis? Only time will tell, and the viability of cultivation will primarily depend on two factors, weather and geography. There are several sources of state-law water rights, depending on the location of the prospective cultivation. The right to take water is a real property interest in California, and water rights are among the most complex areas of property law; they consist of the following: Riparian (Surface Water) Rights. The right of the landowner to take water from a natural watercourse (lake or stream) contiguous to its property for use on the riparian land. Riparian rights are appurtenant to the riparian land and are transferred with the land. Riparian water supplies are sustained by weather (the amount of rainfall and snow-packs). Overlying (Groundwater) Rights. The right of the landowner to take subsurface water that flows beneath or that percolates to the owner's land for use on that land. Some counties have unsustainably low levels of groundwater that led to California’s enactment of the Sustainable Groundwater Management Act in 2014. Appropriative Rights. The right to take surface or subsurface waters in excess of that reasonably used by riparian or overlying owners. Appropriative rights are rights in gross. Since 1914, a person can obtain appropriative rights only by filing an application with the State Water Resources Control Board for a permit to use unappropriated water. Prescriptive Rights. The right to take surface or subsurface waters by meeting the requirements for a prescriptive easement. Prescriptive rights are rights in gross. Pueblo or Communal Rights. Under Spanish, then Mexican, law the pueblo had a right paramount to both riparian or appropriative rights to water flowing through it for as much as was necessary for the supply of its inhabitants. Cities that were successors to the pueblo, such as Los Angeles and San Diego, succeeded to these superior rights to satisfy their municipal needs and those of their inhabitants. This doctrine applies to both surface and subsurface waters.\ The multitude of legal bases for water rights are found in the California Constitution, the common law, statutory law, and state regulations, or a combination of any of these. See specific law sources, summarized in California Easements and Boundaries: Law and Litigation, chap 3 (Cal CEB). But all water rights in California, however acquired, are rarely absolute and are likely subject to: the prohibition against “waste or unreasonable use” of water in the California Constitution, the public trust doctrine (a common law, public policy principle embodied in the state's authority as a sovereign to exercise continuous supervision and control over the navigable waters of the state inuring to the benefit of the state as a whole; and the state policy declared in Water Code §106, which essentially establishes that in California, "the use of water for domestic purposes is the highest use of water and that the next highest use is for irrigation. During periods of drought, any of these principles can be significantly invoked to curtail the volume of water available to holders of riparian and overlying (as well as holders of appropriative) water rights and to protect the environment and wildlife. For more information and analysis on California’s complex water rights’ scheme, legal efforts to balance the interests in these rights, and the constitutional influences on them, see California Easements and Boundaries: Law and Litigation, chap 3 (Cal CEB).