For instance, if in the course of your monitoring program you were to notice that the concentration of lead was decreasing as you moved farther down a watershed, it would be useful to know what happened to the lead. The chemical equilibrium approach would tell you if lead solids were forming or if an observed change in pH was due to the addition of a new ion to solution. If most of the lead is calculated to form a particular solid phase, if might be interesting to see how small perturbations in the system effects the dissolution of lead. By describing the underlying mechanism you are increasing your ability to make decisions about this system. Analytical Insight I'll give you one last example.
Many laboratories routinely analyze water samples for a whole array of ionic constituents.
It is inherent within any type of measurement that a certain amount of uncertainty will be introduced. Many questions come up in this type of work. One of the first checks that researchers perform on a sample is for ion balance. In the actual system, the positive and negative charges will always balance each other out. This is the principle of electroneutrality.