Summary #
Acidity measures the capacity of water to neutralize a base, and in AMD-impacted streams it reflects the total acid load including dissolved metals and hydrogen ions. This page explains what acidity measures, how it differs from pH, and why it is important for treatment system design.
Acidity and pH, although having similarities, should not be confused with each other. pH is a measure of the concentration of free hydrogen ions. This actual concentration of hydrogen ions is a component (often dominant) part of acidity, yet other positively charged ions (cations) also contribute to the acidity of water. Total acidity measures the acidity of the water including both the pH and the other sources of acidity.
Above is a picture of a total acidity test kit from HACH used for field testing. This is a common test kit that is easy to use and read. The directions included with the test are relatively simple and easy to read. This kit will test both free and total acidity. Free acidity will measure the amount of acidity in the water and is reported as the equivalent amount of calcium carbonate (CaCO3) that would be needed for neutralization of the acidity. Total acidity includes calcium carbonate, hydrogen and all other sources of acidity in the water.
HACH Company provides a catalogue of chemical water testing kits and supplies
Other tests, including and/or in addition to those described above, may be appropriate for the watershed in your area. The indicators the were chosen as points of study while making your monitoring plan are a good way to decide what tests need to be performed.
Sources/Links (as provided in the source text):
Related Pages #
- Developing a Monitoring Plan — Structuring your monitoring program
- Buffering (Chemistry Fundamentals) — Alkalinity and buffering capacity
- Acids, Bases, and pH (Chemistry Fundamentals)
Source and Last Reviewed #
Source: AMR Clearinghouse (amrclearinghouse.org). Migrated to AML-Connect. Last Reviewed: 2026-03-13.
[Admin note: Some external links in this article may be outdated. Verify before relying on them. Flag dead links for removal or replacement.]
Tags: acidity, monitoring, sampling, amd
