The total alkalinity of a water is the sum of the bases that are titratable with strong acid:
TA = [HCO3] + 2[CO3] + [B(OH)4] + [OH] + [HPO4] + 2[PO4] + [SiO(OH)3] + [HS] + 2[S] + [NH3] – [H] – [HSO4] – [HF] – [H3PO4]
In seawater alkalinity is roughly equal to the carbonate alkalinity plus borate:
TA = [HCO3] + 2[CO3] + [H2BO3] ,
In most natural freshwaters total alkalinity is roughly equal to the carbonate alkalinity  e.g.:
mHCO3– + 2mCO32-
Bicarbonate (HCO3–) and carbonate (CO32-) ions are derived from weathering reactions. The hydrolysis of bicarbonate and carbonate helps to buffer (or minimise) pH changes caused by photosynthesis.
- Lewis, E., and D. W. R. Wallace. 1998. Program Developed for CO2 System Calculations. ORNL/CDIAC-105. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee.
- Drever, J.I. 1982. The Geochemistry of Natural Waters, Prentice-Hall, Inc., Englewoods Cliffs, N.J., pp. 388.