The local board of health or an official or board designated by local law of such city, as the case may be shall detail, designate or appoint an inspector or inspectors of plumbing, subject, however, to the provisions or limitations of law, regulating the appointment of such inspectors by such board of health or an official or board designated by local law of such city. All inspectors of plumbing who are detailed, designated or appointed shall be practical plumbers and shall not be engaged directly or indirectly in the business of plumbing, during the period of their appointment. They shall be citizens and actual residents of the city in which they are appointed; except in the cities of Cortland and Corning, where such inspectors shall be citizens and actual residents of the county or counties wherein the city is situated, or in an abutting or adjacent county; except in the city of Watertown, where such inspectors shall be citizens and actual residents of the county wherein the city is situated except in the city of Middletown, where such inspectors shall be citizens and actual residents of the county wherein the city is situated, or within a twenty-five mile radius of the city of Middletown as long as such inspectors are citizens and actual residents of this state; except in the city of Jamestown, where such inspectors shall be citizens and actual residents of the county wherein the city is situated; except in the city of Tonawanda, where such inspectors shall be citizens and actual residents of the county wherein the city is situated, or in an abutting or adjacent county; except in any city with a population of less than twenty-five thousand, where such inspectors shall be citizens and actual residents of the county or counties wherein the city is situated. Before entering upon the discharge of their duties as such inspectors they shall each be required to obtain a certificate of competency from said examining board. They shall be entitled to receive compensation to be fixed by the officer, board, commission or department having power to fix salaries generally or, if there be no officer, board, commission or department thereof having such power, by the board of aldermen or common council.