Twenty-First Century Water Commission Act of 2007

Establishes the Twenty-First Century Water Commission to: (1) use studies and assessments to project future water supply needs and demand, develop national and regional assessments on flood risk and water availability and trends related to water quality; (2) study government and private sector water management programs directed at increasing water supplies, managing flood risk, and improving the availability, reliability, and quality of water resources; and (3) develop recommendations for a comprehensive water strategy.

Requires such strategy to: (1) identify incentives to ensure an adequate and dependable supply of water to meet U.S. needs for the next 50 years; (2) consider all available technologies and methods to optimize water supply reliability, availability, and quality, while safeguarding and enhancing the environment; (3) suggest financing options for development of comprehensive watershed management plans, regional watershed planning, holistically designed water resources projects, and increased use of nonstructural elements (including green infrastructure and low impact development techniques); (4) encourage the integration of flood control and water supply projects, including recommendations for capturing excess water and flood water for conservation and reuse; (5) suggest options to promote the use of, and reduce biases against, nonstructural elements when managing stormwater; and (6) encourage the avoidance and minimization of adverse impacts to, and the restoration of, natural systems.

Directs the Commission, in developing such strategy, to: (1) evaluate the effectiveness of hazard mitigation strategies and contingency planning provisions for water management programs in light of climate change impacts; (2) evaluate such impacts; (3) include strategies for using best available climate science in projections of future flood and drought risk and for developing hazard mitigation strategies to protect water quality in extreme weather conditions caused by climate change; (4) identify adaptation techniques, or further research needs of such techniques, for responding to climate change impacts; (5) respect the primary role of states in adjudicating, administering, and regulating water rights and water uses; (6) identify whether recommendations are consistent with existing laws; (7) identify duplication among federal governmental programs and make recommendations to improve coordination among federal, interstate, state, and local agencies; and (8) avoid suggesting increased mandates on state and local governments.

Requires the Commission to submit interim and final reports to the President and Congress. Terminates the Commission 30 days after its transmission of a final report. Authorizes appropriations.