What is reagent water?

• A. Water that is only used for cleaning glassware.
• B. Water that contains some reagents.
• C. Water with dissolved salts to adjust conductivity.
• D. Water with no detectable concentration of the component to be analyzed and that is free of substances that interfere with the method.

Answer: (D)

Reagent water is water that has been purified to such a high level that it won’t affect the outcome of an analysis. When you prepare reagents, calibrators, or samples, you don’t want anything in the water to add the analyte you’re trying to measure or to introduce substances that could change the method’s signal. So reagent water is defined as water with no detectable concentration of the component being analyzed and free of substances that would interfere with the method. That means extremely low levels of ions, organic compounds, particulates, or reactive species that could skew results.

This isn’t just about cleanliness or taste; it’s about ensuring accuracy and reliability of measurements. Water used only for cleaning glassware, water with reagents in it, or water deliberately adjusted with salts would introduce contaminants or alter the assay, making it unsuitable as reagent water.