Reclamation Reform Act of 1991 - Amends the Reclamation Reform Act of 1982 to revise and add certain definitions, including definitions of "landholding," "custom farmer," "active farmer," and "operation" as they apply under such Act. Makes changes to provisions concerning: (1) water service contracts; (2) pricing; (3) certification as a condition to the receipt of irrigation waters; (4) the application of ownership and pricing limitations to trusts; (5) landholdings of religious and charitable organizations; and (6) enforcement of payment for delivery of irrigation to landholders.

Directs the Secretaries of the Interior and Agriculture to negotiate and execute a memorandum of understanding to permit the Secretary of the Interior access to, and use of, information collected and maintained by the Department of Agriculture which would aid enforcement of the ownership and pricing limitations of Federal reclamation law, including the Reclamation Reform Act of 1982.