Water System Adaptation Partnerships Act of 2009 - Directs the Administrator of the Environmental Protection Agency (EPA) to make grants to water systems to assist in planning, designing, constructing, implementing, or maintaining any program, strategy, or infrastructure improvement to: (1) conserve water or increase water use efficiency; (2) carry out water metering to measure water efficiency effectiveness of a water efficiency program; (3) preserve or improve water quality; (4) enhance water management by increasing source water preservation and protection, or natural or engineered green infrastructure, in the management, conveyance, or treatment of water, wastewater, or stormwater; (5) increase energy efficiency or the use and generation of renewable energy in the management, conveyance, or treatment of water, wastewater, or stormwater; (6) support the adoption and use of advanced water treatment, water supply management, or water demand management technologies or processes that maintain or increase water supply or improve water quality; (7) complete studies or assessments to project how climate change may impact the future operations and sustainability of the water system; or (8) carry out any other activity or project to address any ongoing or forecasted climate-related impact on the water quality or quantity of a region of the United States that increases the resiliency of a water system to the impacts of climate change.
Sets forth grant application requirements. Requires the Administrator to conduct a competitive process to select and fund applications, giving priority to applications that: (1) are submitted by water systems that are at the greatest and most immediate risk of facing significant climate-related negative impacts; (2) will impact the largest numbers of water users; and (3) will provide the greatest benefit per dollar expended. Limits the federal share to 50% of the cost.