Irvine Basin Surface and Groundwater Improvement Act of 2003 - Amends the Reclamation Wastewater and Groundwater Study and Facilities Act to authorize the Secretary of the Interior, in cooperation with the Irvine Ranch Water District, California, to participate in the design, planning, and construction of projects to naturally treat impaired surface water, reclaim and reuse impaired groundwater, and provide brine disposal within the San Diego Creek Watershed.