Alkalinity

Alkalinity is a measure of water's ability to neutralize acids, and so is related to pH. It results primarily from dissolving limestone or dolomite minerals in the aquifer.

Don’t confuse alkalinity with pH. pH measures the strength of an acid or base; alkalinity indicates a solution’s power to react with acid and "buffer" its pH— that is, the power to keep its pH from changing. Alkalinity is important for fish and aquatic life because it protects or buffers against pH changes (keeps the pH fairly constant) and makes water less vulnerable to acid rain. The main sources of natural alkalinity are rocks, which contain carbonate, bicarbonate, and hydroxide compounds. Borates, silicates, and phosphates may also contribute to alkalinity.

Limestone is rich in carbonates, so waters flowing through limestone regions generally high alkalinity— hence its good buffering capacity. Conversely, granite does not have minerals that contribute to alkalinity. Therefore, areas rich in granite have low alkalinity and poor buffering capacity.