Alkalinity measures the acid-neutralizing capacity of a water sample. It is an aggregate property of the water sample and can be interpreted in terms of specific substances only when a complete chemical composition of the sample is also performed. The alkalinity of surface waters is primarily
due to the carbonate, bicarbonate, and hydroxide content and is often interpreted in terms of the concentrations of these constituents. The higher the alkalinity, the greater the capacity of the water to neutralize acids; conversely, the lower the alkalinity, the less the neutralizing capacity. To detect the different types of alkalinity, the water is tested for phenolphthalein and total alkalinity, using Equations:

Phenolphthalein alkalinity (mg/L) as CaCO3=A x N x 50,000/mL of Sample

Total alkalinity (mg/L) as CaCO3=B x N x 50,000/mL of Sample

where
A= titrant (mL) used to pH 8.3
B= titrant (mL) used to titrate to pH 4.5
N= normality of the acid (0.02N H2SO4 for this alkalinity test)
50,000 = a conversion factor to change the normality into units of CaCO3