To install, repair, or alter complete plumbing systems which shall include supply water piping systems, waste water piping systems, fuel gas piping systems, and other fluid piping systems; the equipment, instrumentation, non-electric controls, and the fixture for these systems and the venting for waste water piping systems and fuel gas piping systems; for any purpose in connection with the use and occupancy of buildings, structures, works, and premises where people or animals live, work, and assemble; including piping for vacuum, air, and medical gas systems, spas and swimming pools, lawn sprinkler systems, irrigation systems, sewer lines and related sewage disposal work performed within property lines, fire protection sprinkler systems when supervised by licensed mechanical engineers or licensed fire protection contractors, and solar hot water heating systems, and the trenching, back filling, patching, and surface restoration in connection therewith.