Which contaminants are listed for quarterly water quality testing?

• A. Copper
• B. Lead
• C. Arsenic
• D. Copper, Lead, Arsenic, Mercury

Answer: (D)

The test checks which contaminants are required to be monitored on a quarterly basis to protect drinking water health. These four—copper, lead, arsenic, and mercury—are the set specified for quarterly testing because they cover common pathways of exposure in typical building water systems: lead and copper from aging or corroded piping, arsenic from natural groundwater sources, and mercury from certain legacy devices or process sources. Regularly measuring these four helps quickly detect any spikes, enabling timely actions such as adjusting corrosion control, treating the water, or replacing plumbing to keep the water safe for occupants. Testing only one of them wouldn’t provide the comprehensive check the standard requires, so the combination of all four is the correct and best-fit answer.