No person shall engage in work or the conduct of the business of plumbing or landscape irrigation within the city, except as herein specifically exempted, unless such person is the holder of a valid license as issued by the Texas Board of Plumbing Examiners or the Texas Board of Irrigators. Plumbing work by a landscape irrigation installer, however, is limited to the installation and repair of irrigation systems and connection of these systems to the customer's side of the water service. Nothing contained herein shall prohibit the employment of a journeyman plumber or irrigator or apprentice to engage in plumbing work under the general supervision of a master plumber nor plumbing work done by a property owner in a building or on a premises owned or occupied by him as his home.