Buy American Improvement Act of 2017 This bill amends the Buy American Act and federal grant programs to: (1) standardize guidelines for federal agencies to waive Buy American requirements for their construction contracts and direct purchases of materials for public buildings, uses, or works; and (2) extend domestic content requirements to additional grant programs that federal agencies administer to fund states and other entities carrying out transportation and infrastructure projects. The Office of Federal Procurement Policy (OFPP) must require agencies to: (1) publicly disclose and justify their Buy American waivers, (2) ensure projects are not disaggregated to avoid such requirements, (3) be subject to investigations for improper waivers, and (4) minimize waivers that would decrease employment in the United States. The bill: (1) directs the OFPP to issue rules to evaluate domestic content in "manufactured end product," (2) requires domestic component costs to exceed 75% before manufactured materials are considered manufactured "substantially all" from U.S. materials, (3) excludes project start-up costs from a domestic offer in comparisons of offers between domestic and nondomestic entities, (4) prohibits agencies from determining that the acquisition costs of U.S. materials is unreasonable unless it would increase overall acquisition cost by more than 25%, and (5) applies Buy American requirements to materials for use outside the United States that are not needed on an urgent basis or that are acquired on a regular basis. An agency is prohibited from determining that a material is not mined, produced, or manufactured in the United States in sufficient and reasonably available commercial quantities and of a satisfactory quality unless: (1) domestic production cannot be initiated without significantly delaying the project; and (2) a substitutable material is not in the United States in sufficient and reasonably available commercial quantities and of a satisfactory quality. The bill amends the American Recovery and Reinvestment Act of 2009 to require the Department of Homeland Security to procure from U.S. sources certain national security items used to construct border protection barriers and roads under the Illegal Immigration and Reform and Immigrant Responsibility Act of 1996. The bill prohibits the Federal Highway Administration (FHWA) from waiving Buy America requirements for states applying to use federal-aid funds to purchase buses, vehicles, or other rolling stock under the Congestion Mitigation and Air Quality Improvement Program unless: (1) the cost of components and subcomponents produced in the United States is more than 60% of the cost of all components of the rolling stock; and (2) final assembly of the rolling stock has occurred in the United States. The bill requires involvement by the National Institute of Standards and Technology and a domestic supplier scouting process for domestic content waivers that: (1) the Federal Railroad Administration (FRA) issues to Amtrak for rail projects, and (2) the Federal Aviation Administration (FAA) issues to grant recipients under the airport improvement program. The FAA may approve an airport improvement project financed with passenger facility charges only if the steel and manufactured goods are produced in the United States. The bill amends the Safe Drinking Water Act, the Department of Agriculture Reorganization Act of 1994, the Housing and Community Development Act of 1974, the Rural Water Supply Act of 2006, the Federal Water Pollution Control Act (commonly known as the Clean Water Act), and the Railroad Revitalization and Regulatory Reform Act of 1976 to add domestic source requirements, and require public notice and comment before any waivers of such requirements, for projects supported by: the Environmental Protection Agency's grants to state drinking water treatment or water pollution control revolving loan funds; the Rural Utilities Service; the Department of Housing and Urban Development; the Department of the Interior for the construction of treatment works for rural water projects; or the FRA.