pH is a measure of the acid content of the water sample. This meter also uses an oxidation-reduction reaction to detect the presence and amount of hydrogen ion (H⁺) in the sample. Typical river water values range from 5 to 7. Sites with high conductivity often have pH’s as high as 8.2. Acidification of natural waters is a result of acid rain entering waters with little buffering ability (see Alkalinity). Local industries and the power plant contribute to this as well. Fish experience stress at pH’s below 5.

Alkalinity is a measure of the acid buffering ability of a water sample. The main chemical agents responsible for buffering are carbonate (CO₃^2-) and bicarbonate (HCO₃^-). If acid (H⁺) is put into the sample, the following buffering reactions occur:

First, H⁺ + CO₃^2- = HCO₃^-

Then when all of the carbonate is gone (pH will be below 6 at this point): H⁺ + HCO₃^- = H₂CO₃

Other negatively charged compounds can act as buffers, such as borate, nitrate, organic acids, but are present at such low concentrations as to be relatively insignificant.

As mentioned above in the pH section, alkalinity is important to measure as it quantifies the ability of a water body to resist acidification. Alkalinity is measured by measuring the amount of acid required to lower the pH of a water sample to a value of 4.5, the point at which all of the carbonate and bicarbonate buffers have been exhausted. The concentration units are mg Calcium Carbonate (CaCO₃) per liter of water or ppm CaCO₃. Typical river water values range from 5 to 15. Values above 15 indicate high total dissolved solids levels associated with stormwater runoff.

The US EPA uses the following categories to classify water bodies by their alkalinity: