During a routine inspection of a commercial building, a plumber identifies a cross-connection between the potable water supply and a non-potable rainwater harvesting system. What is the immediate and most critical action the plumber should take?

Question: During a routine inspection of a commercial building, a plumber identifies a cross-connection between the potable water supply and a non-potable rainwater harvesting system. What is the immediate and most critical action the plumber should take?

Answer options: ✅ Shut off the potable water supply to the building immediately.

• Install a double check valve assembly (DCVA) at the cross-connection.
• Apply warning labels to both the potable and non-potable lines.
• Advise the building owner to test the water quality weekly.

Correct answer: Shut off the potable water supply to the building immediately.

Explanation: A direct cross-connection between potable and non-potable water systems poses an immediate and severe health risk due to potential contamination of the drinking water. Shutting off the potable supply is the fastest way to eliminate immediate danger. While installing a backflow preventer is a long-term solution, immediate action to prevent contamination is paramount.