D.C. Code § 34-2401.23: Main pipes; laying for use of public buildings.

No greater number of main pipes of the Washington Aqueduct shall be laid at the expense of the United States than are sufficient to furnish the public buildings, offices, and grounds with the necessary supply of water. The cost of any main pipe, for the supply of water to the inhabitants of Washington, must be paid by the District of Columbia, in the manner provided by law.