Tualatin River Basin Water Supply Enhancement Act of 2003 - Authorizes the Secretary of the Interior, acting through the Bureau of Reclamation, to conduct a water supply feasibility study of the Tualatin River Basin in Oregon in order to identify: (1) ways to meet future water supply needs; (2) water conservation and storage measures; (3) measures that would improve water quality and enable environmental and species protection; and (4) integrated water resource management and supply needs.