Alkalinity (as CaCO3)
What This Measurement Means
Alkalinity is not a contaminant and not a chemical — it is a property. USGS defines it as "the buffering capacity of a water body; a measure of the ability of the water body to neutralize acids and bases and thus maintain a fairly stable pH level", and notes it depends on the presence of bicarbonates, carbonates and hydroxides. It is reported as mg/L (or ppm) of calcium carbonate. Higher alkalinity means the water resists sudden pH swings. EPA sets neither a health limit (MCL/MCLG) nor a secondary standard for alkalinity, so there is no threshold at which a reading becomes unsafe to drink — the number is context for corrosivity, treatment and taste, not a safety verdict.
Source: USGS — Water Science School (retrieved 2026-07-27)
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Contaminant Type
Alkalinity (as CaCO3) is classified as a Properties contaminant.
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