The orifice of a drinking fountain shall be provided with a protective __________ to prevent contamination of potable water supply system.

The orifice of a drinking fountain must be equipped with a protective cowl to ensure that the potable water supply system remains uncontaminated. A cowl serves as a protective hood that covers the outlet, preventing debris, insects, and other contaminants from entering the water stream. This design feature is critical in maintaining water quality and safety, particularly in public areas where drinking fountains are commonly used.

While a cover, grate, or shield might suggest some form of protection, they do not provide the same specific functionality as a cowl in the context of a drinking fountain's design requirements. A cover can simply block access but may not effectively prevent contamination as water is being dispensed. A grate is typically used for drainage and wouldn't be appropriate for this application. A shield, while also protective, may not address the specific needs of keeping contaminants out of a drinking fountain's water outlet in the same effective manner that a cowl does. Thus, a cowl is the most recognized and appropriate method for safeguarding drinking water in this scenario.