To amend the San Luis Rey Indian Water Rights Settlement Act, and for other purposes.

Amends the San Luis Rey Indian Water Rights Settlement Act to direct the Secretary of the Interior, as an alternative by which to provide a supplemental water supply for the benefit of certain Mission Indian Bands in San Diego County, California, and the City of Escondido, California, the Escondido Mutual Water Company, and the Vista Irrigation District (local entities) to construct that portion of the All-American Canal Lining that is necessary to conserve 16,000 acre-feet of water per year and arrange to deliver such water to the Bands and such local entities by exchange or through contract with the Metropolitan Water District of Southern California and other parties with conveyance facilities. Requires the right to such water to be held in perpetuity by the United States in trust for the San Luis Rey Indian Water Authority subject to such Act and the settlement agreement governing the use and disposition of supplemental water. Authorizes appropriations for such construction, but prohibits Federal funding for operating, maintenance, or replacement costs. Directs the Secretary to determine the impact of such works constructed on the cost of operation and maintenance and the existing regulating and storage capacity of the All-American Canal and its Coachella Branch. Requires, if the works result in any added operation and maintenance costs which exceed the benefits derived from increasing the regulating and storage capacity of the canals to the Imperial Irrigation District or the Coachella Valley Water District, the Indian Water Authority and the local entities shall reimburse the agency which experiences such additional costs on an annual basis pursuant to the Secretary's determination.

States that the right to 16,000 acre-feet of water per year obtained by such construction is subject to such works being maintained so as to continue to conserve 16,000 acre-feet of water per year as compared to the situation that existed prior to the construction. Provides for the Secretary to determine the amount of water so conserved on an ongoing basis and to allow only such water as has actually been conserved to be delivered to the Indian Water Authority and the local entities.