Milliequivalents per Liter

Definition

A concentration unit expressing reactive charge per liter, where one meq/L of positive charge always balances one meq/L of negative charge.

Alkalinity as mg/L as CaCO3 converts directly to meq/L by dividing by 50, since 50 mg/L as CaCO3 equals 1 meq/L. A mole counts molecules while an equivalent counts reactive charge, so meq/L tells you how much chemistry the water can actually do. Reporting hardness and alkalinity in meq/L lets them be compared on the same charge basis without separate molecular-weight conversions.

Related concepts

Hardness as CaCO3 · mg or L as Calcium Carbonate · Equivalent Weight

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Part of The Blueprint of Water · 📏 measurement