The alkalinity result is expressed as which unit?

• A. Mg/L OH-
• B. Alk (mg/L CaCO3)
• C. ppm CaCO3
• D. mg/L CaCO3 equivalent

Answer: (B)

Alkalinity is the water’s buffering capacity against acids, coming mainly from bicarbonate, carbonate, and hydroxide ions. To compare this buffering power consistently, it’s expressed as calcium carbonate equivalents. The standard unit is milligrams per liter as calcium carbonate (mg/L CaCO3), sometimes written as Alk (mg/L CaCO3). This convention lets you interpret the value as the amount of CaCO3 that would neutralize the same amount of acid per liter, regardless of which species contributes to the alkalinity. Other options either describe a specific constituent (like hydroxide) or use alternative wording that isn’t the typical reporting form, while mg/L CaCO3 is the widely recognized expression.