Notwithstanding any other provision of this chapter, the right to extract sodium chloride, contained in any lands belonging to the State, or which may become the property of the State, situate in any of the townships described in Section 6931, which may be necessary or convenient for use in conditioning a public water supply owned, controlled, or operated by any metropolitan water district of the State, may be sold at a reasonable price or royalty, or both, to be fixed by the commission and conveyed to any such metropolitan water district.