Modifications to the Pima County Wastewater Management Regional Treatment System for Improved Reclaimed Water Production Act - Amends the Reclamation Wastewater and Groundwater Study and Facilities Act to authorize the Secretary of the Interior, in cooperation with Pima County, Arizona, to participate in the planning, design, and construction of modifications to water recycling facilities and to provide advanced treatment for production of reclaimed water for use in environmental restoration, recharge and reclaimed water projects for the towns, cities, and unincorporated areas of Pima County. Limits the federal share to 25% of the cost of the project. Prohibits the use of federal funds for project operation or maintenance.