Alkalinity: The capacity of water to neutralize acids. This capacity is caused by the water’s content of carbonate, bicarbonate, hydroxide and occasionally borate, silicate, and phosphate. Alkalinity is expressed in milligrams per liter of equivalent calcium carbonate. Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have a high alkalinity. Alkalinity is a measure of how much acid can be added to a liquid without causing a great change in pH.” – EPA Vocabulary Catalog

“What is total alkalinity and why is it important?

Alkalinity is a measure of the capacity of water to neutralize acids… Alkaline compounds in the water such as bicarbonates (baking soda is one type), carbonates, and hydroxides remove H+ ions and lower the acidity of the water (which means increased pH). They usually do this by combining with the H+ ions to make new compounds. Without this acid-neutralizing capacity, any acid added to a stream would cause an immediate change in the pH. Measuring alkalinity is important in determining a stream’s ability to neutralize acidic pollution from rainfall or wastewater. It’s one of the best measures of the sensitivity of the stream to acid inputs.

Alkalinity in streams is influenced by rocks and soils, salts, certain plant activities, and certain industrial wastewater discharges.” –EPA Archive

Sources of alkalinity in water:

In the absence of other pollutants, alkalinity is affected by the types of rock and soil water is exposed to. Wells drilled in carbonate-type rocks create water with higher alkalinity. Alkalinity in streams is influenced by rocks and soils, salts, certain plant activities, and certain industrial wastewater discharges.

Health Limits:

Not regulated for health in USA
In Canada, the operational guideline (aesthetic target) for water treatment plants in Canada is 30-500 mg/L.

Additional Resources:

Wikipedia – “Alkalinity” (webpage)

MEL Test Method for Alkalinity by Titration:

Standard Methods, 18th Edition – Methods 2320B and 2320B/M*
Standard Methods, 22nd Edition – Methods 2320B and 2320B/M*

* approved for SDWA and NPDES compliance

Sample Requirements for Alkalinity testing:

Container: plastic, glass
Min. Volume: 250 mL
Temp.: cold ≤6°C
Hold time: 14 days