Which water characteristic refers to the ability of water to neutralize acids?

• A. Alkalinity
• B. Acidity
• C. Hardness
• D. Dissolved Gases

Answer: (A)

Alkalinity is the water’s buffering capacity—the amount of acid the water can neutralize before its pH begins to drop. This buffering comes mainly from bases like bicarbonate, carbonate, and hydroxide ions, which react with added hydrogen ions (acid) to form weaker acids or water. In most natural waters, bicarbonate is the major contributor: when acid is introduced, bicarbonate converts to carbonic acid, which then becomes carbon dioxide and water, absorbing the extra hydrogen ions and limiting pH change. That buffering action is what we mean by the ability to neutralize acids. Acidity is about the present acid content and the tendency to lower pH, not the water’s capacity to resist pH change; hardness involves calcium and magnesium ions and affects scaling rather than buffering; dissolved gases influence gas content and can affect pH but don’t define the acid-neutralizing capacity.