Rio Grande Water Security Act This bill requires the Department of the Interior to develop and implement an integrated water resources management plan (i.e., the Basin Plan) for the Rio Grande Basin and reauthorizes an irrigation infrastructure grant program for Rio Grande Pueblos tribes. Specifically, Interior must convene a working group of designated federal agencies to collaborate with the Basin States (Colorado, New Mexico, and Texas), Indian tribes, local governments, irrigation districts, and other partners to develop and implement a plan for improving the basin's water security and quality, river and watershed health, and resilience to drought. The plan must include (1) project recommendations for updating reservoir operations, increasing water conservation, and improving infrastructure; (2) a list of potential changes that may be needed to existing federal authorities to implement the plan; and (3) a 30-year implementation time line. After the plan is submitted to Congress, relevant agencies may implement recommended projects. Agencies may also waive cost-sharing requirements for projects that demonstrate significant public benefits. The bill also reauthorizes an irrigation infrastructure grant program that permits the Bureau of Reclamation to provide grants and enter into agreements with the Rio Grande Pueblos tribes for repairing and replacing Pueblo irrigation infrastructure to (1) increase water use efficiency and agricultural productivity, (2) conserve water, and (3) enhance water management.