Western Water Supply Enhancement Act

Western Water Supply Enhancement Act - Amends the Omnibus Public Land Management Act of 2009 to direct the Secretary of the Interior, in calculating the non-federal share of the cost of an infrastructure improvement or activity proposed by an eligible applicant for a water management improvement grant or agreement, to consider: (1) non-federal funds secured and committed to the planning, design, or construction of improvements authorized for research activity funding, even if such funds are secured and committed in advance of an application for such a grant or agreement; and (2) amounts that the applicant receives from federal power marketing agencies.

Directs the Secretary to provide such a grant or agreement to assist any eligible applicant in planning, designing, or constructing any water management improvements as part of a multiyear regional, integrated, and coordinated water conservation and management plan. Requires an applicant, in order to be eligible for such a grant or agreement, to: (1) be located in Arizona, California, Colorado, Idaho, Kansas, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, Texas, Utah, Washington, Wyoming, American Samoa, Guam, the Northern Mariana Islands, or the Virgin Islands; and (2) submit to the Secretary an application that includes a long-term (minimum of five years) water conservation and management plan based on a regional, coordinated, and integrated water conservation and management model for either an entire watershed or river basin or a regional effort that includes multiple partnering irrigation or municipal entities and a proposed budget and schedule for improvements or activities to be planned, designed, constructed, or implemented by the applicant consistent with the plan submitted.

Limits the amount provided to a grant or agreement applicant to $15 million for each five-year period. Directs the Secretary to consider providing at least one grant to two of the five Reclamation Regions having submitted a valid grant application.