What must be installed to protect against backflow when the water source's use is unknown?

To protect against backflow when the water source's use is unknown, a reduced pressure zone assembly is the most effective choice. This assembly is specifically designed to prevent contamination of the potable water supply from potentially hazardous substances.

The reduced pressure zone assembly functions by maintaining a constant pressure that is lower than the supply line pressure, thereby preventing any backflow of water into the clean water supply. It incorporates two check valves and a pressure differential relief valve, allowing it to handle various situations where backflow could occur, such as variations in water use or pressure changes.

The necessity for such a robust solution stems from the potential risks associated with unknown water sources. If those sources could introduce contaminants or non-potable substances, a strong backflow prevention mechanism like a reduced pressure zone assembly is crucial. This level of protection is mandated in many plumbing codes when the risk of contamination is present.

In comparison, while options like an air gap or check valve can provide backflow prevention, they may not offer the same level of protection against the complex threats posed by a potentially unknown water source. An air gap is effective in straightforward situations, but reduced pressure zone assemblies are more suited for high-risk scenarios. Check valves help prevent backflow in specific instances but do not address pressure fluctuations