Twenty-First Century Water Commission Act of 2009 - Establishes the Twenty-First Century Water Commission to: (1) project future water supply and demand; (2) study current water management programs of federal, interstate, state, and local agencies and private sector entities directed at increasing water supplies and improving the availability, reliability, and quality of freshwater resources; and (3) consult with representatives of such agencies and entities to develop recommendations for a comprehensive water strategy. Requires that such strategy: (1) identify incentives intended to ensure an adequate and dependable water supply to meet U.S. needs for the next 50 years; (2) suggest strategies that avoid increased mandates on state and local governments, considering all available technologies; and (3) suggest financing options.