Cal. Water Code § 71757

To carry out the purposes of this division, a district shall have the power to commence, maintain, intervene in, defend and compromise, in the name of the district, or as a class representative of the inhabitants, property owners, taxpayers, water producers or water users within the district, or otherwise, and to assume the costs and expenses of any and all actions and proceedings now or hereafter begun to determine or adjudicate all or substantially all of the water rights of a basin or other hydrologic unit overlain, in whole or in part, by the district, as between owners of or claimants to such rights, to prevent any interference with water or water rights used or useful to the lands, inhabitants, owners, operators, or producers within the district, or to prevent the diminution of the quantity or quality of the water supply of the district or such basin, or to prevent unlawful exportation of water from the district or such basin.