In those parts of Prince George’s County that are not in the sanitary district, the Commission’s plumbing regulations: apply to plumbing installations that began on or after June 1, 1965; but do not apply to plumbing installations that existed on July 1, 1965. The owner of the property where plumbing installations existed on July 1, 1965, is not required to change the plumbing until water or sewer service is obtained from a Commission system. If water or sewer service is obtained from a Commission system, this section and the Commission’s regulations apply to the property and the plumbing as if the property were in the sanitary district. The Commission may enter into an agreement with Prince George’s County under which the county will issue the necessary permit and perform the necessary inspection for and in the name of the Commission in those areas that are not in the sanitary district, if the agreement provides that the plumbing regulations of the Commission will be applied. This subsection or an agreement entered into under this subsection does not affect the power of the Commission: to adopt regulations to install plumbing in Prince George’s County as the Commission considers necessary for the public health; or to regulate public and semipublic water supply and sewer systems under this section and § 24–102 of this subtitle.