Step 4: Carbonate System and Calcite Saturation

Buffer Capacities & Alkalinity


All relevat information about the carbonate system, buffer capacities, alkalinity, and water hardness are summarized in the right screenshot.1

The upper part show the calculated buffer capacities (ANC and BNC). For each capacity two values are given:

If thermodynamics forbids any precipitation both values are equal.2

Additional information shown in this panel are:

For more information see here.

Calcite Saturation


This screenshot refers to the calcite-carbonate system:3

In addition, the CO2 (carbonic acid) is split into “free” CO2 and “bound” CO2. This allows to quantify the

In the given example the water tends to be corrosive (i.e. the water dissolves calcite). The corresponding saturation index as well as the calcium carbonate precipitation potential are both negative. The water has 38.9 mg/L CO2 in excess.


  1. This panel is the left part of a larger window shown here

  2. In the present example the amount of precipitated Fe(OH)3 is too small to have a noticeable impact on ANC and/or BNC. 

  3. This panel is the right part of a larger window shown here

[last modified: 2014-11-16]