What is an essential characteristic of a Reduced Pressure Zone (RPZ) assembly?

A Reduced Pressure Zone (RPZ) assembly is designed to provide protection against backflow in a plumbing system. Its essential characteristic is that it contains two check valves and a relief valve.

The two check valves work together to prevent contaminated water from flowing back into the clean water supply. If either of the check valves were to fail, the relief valve—situated between them—will open and discharge water, preventing back pressure and ensuring the system remains safe and effective. This configuration is crucial for maintaining the integrity of the potable water supply by creating a barrier against potential contaminants that could enter the system.

The other options do not accurately define core characteristics of an RPZ assembly. For example, while RPZ assemblies can be installed underground, they are not limited to that setting; they can also be installed above ground as long as the assembly is accessible for maintenance. Additionally, these assemblies do not require manual operation; they function automatically based on water pressure changes. Maintenance is indeed necessary to ensure the RPZ operates effectively; neglecting it can lead to malfunctions and potential safety hazards. Thus, the inclusion of two check valves and a relief valve is what clearly establishes the function and safety features of an RPZ assembly.