Guidance for Charge-Balance Adjustment
Sometimes we want to know which chemical parameter of a given water sample is the primary cause of the CBE. Unfortunately, there is no general answer to this question. What we can do, however, is to narrow down the number of potential candidates.
One decision method is based on the interplay between CBE on the one hand and EC (or equivalently TDS) on the other hand. The direct comparison between the measured and calculated EC (or TDS) tells us whether the analysis contains too much or too little anions/cations.
For example: The right image shows a water sample with negative CBE (i.e. more anions than cations). The “Guidance for charge-balance adjustment” (which opens by the button Details) recomments the type of ions as follows:
If the measured EC is greater than the calculated EC (here 245 µS/cm) cations are deficient. Thus, select one cation: Ca, Mg, Na, or K.
Otherwise: If the measured EC is less than the calculated EC (here 245 µS/cm) there are too much anions. Thus, select one anion: DIC, sulfate, chloride, or nitrate.
Two questions arise:
1. What happens if I act against the recommendation?
Then, the discrepancy between the measured and calculated EC (or TDS) will increase.
2. What about pH as parameter?
Of course, with the “default parameter” pH you always achieve charge balance. However, in practice the pH is often measured with sufficient accuracy, whereas some concentrations may be more problematic.
Note. The guidance/recommendation makes only sense for validity-checks of water analyses where measured values of EC and/or TDS are available.
[last modified: 2014-02-02]