Mo. Rev. Stat. § 144.058
In addition to the other exemptions granted pursuant to this chapter, there is hereby specifically exempted from the provisions of and the computation of the tax levied, assessed, or payable pursuant to this chapter and the local sales tax law as defined in section 32.085, electrical energy and gas, whether natural, artificial, or propane; water, coal, and energy sources; chemicals, machinery, equipment, parts, and material used or consumed in connection with or to facilitate the generation, transmission, distribution, sale, or furnishing of electricity for light, heat, or power; and any conduits, ducts, or other devices, materials, apparatus, or property for containing, holding, or carrying conductors used or to be used for the transmission of electricity for light, heat, or power service to consumers. The provisions of this section shall be in addition to any other sales or use tax exemption provided by law. Any public utility, as such term is defined in section 386.020, that realizes any savings as a result of the sales tax exemption provided in this section shall provide the public service commission information on the amount of savings realized in such public utility's next general rate proceeding and shall include a statement that such savings will be passed through to the public utility's rate revenue requirement determined in the public utility's next general rate proceeding. As used in this section, savings realized shall be calculated as the difference between sales tax incurred and sales tax expense included in current rates.
§ 144.058, RSMo