Waterway LNG Parity Act of 2019 This bill amends the Internal Revenue Code to provide for an energy equivalent for a gallon of diesel, in the case of liquefied natural gas (LNG), for the purposes of the 29 cents per gallon Inland Waterways Trust Fund financing rate. (The rate is used for the excise tax on fuel used in commercial transportation on inland waterways.) The bill specifies that the energy equivalent of a gallon of diesel is 6.06 pounds of LNG.