It shall be the responsibility of all water users to prevent contamination of or damage to water meters or water systems by reason of their operation of the water outlets and water equipment, and if required by the city, the water users shall install, at their expense, check valves, surge tanks, backflow prevention devices, or other devices as prescribed by the Director of Public works in order to avoid damage to or contamination of the meters or systems. Check valves and back flow prevention devices must be tested when installed and annually thereafter at customer's expense.
(`67 Code, § 4-6-5)