Mo. Rev. Stat. § 701.031
Property owners of all buildings where people live, work or assemble shall provide for the sanitary disposal of all domestic sewage. Except as provided in this section, sewage and waste from such buildings shall be disposed of by discharging into a sewer system regulated pursuant to chapter 644, or shall be disposed of by discharging into an on-site sewage disposal system operated as defined by rules promulgated pursuant to sections 701.025 to 701.059. Any person installing on-site sewage disposal systems shall be registered to do so by the department of health and senior services. The owner of a single-family residence lot consisting of three acres or more, or the owner of a residential lot consisting of ten acres or more with no single-family residence on-site sewage disposal system located within three hundred sixty feet of any other on-site sewage disposal system and no more than one single-family residence per each ten acres in the aggregate, except lots adjacent to lakes operated by the Corps of Engineers or by a public utility, shall be excluded from the provisions of sections 701.025 to 701.059 and the rules promulgated pursuant to sections 701.025 to 701.059, including provisions relating to the construction, operation, major modification and major repair of on-site disposal systems, when all points of the system are located in excess of ten feet from any adjoining property line and no effluent enters an adjoining property, contaminates surface waters or groundwater or creates a nuisance as determined by a readily available scientific method. Except as provided in this section, any construction, operation, major modification or major repair of an on-site sewage disposal system shall be in accordance with rules promulgated pursuant to sections 701.025 to 701.059, regardless of when the system was originally constructed. The provisions of subdivision (2) of subsection 1 of section 701.043 shall not apply to lots located in subdivisions under the jurisdiction of the department of natural resources which are required by a consent decree, in effect on or before May 15, 1984, to have class 1, National Sanitation Federation (NSF) aerated sewage disposal systems.
§ 701.031, RSMo