We are a private well water ...

We are a private well water quality management company. We do water quality testing (baseline tests include "standard" drinking water quality parameters (bacteria and nitrates, inorganic chemicals, pH, hardness, etc.), plus radon and VOCs - done at certified laboratories). We encourage annual re-testing, but are considering developing a simple monitor that would track an indicator parameter - such as TDS - that, if changed significantly (e.g., 20%), would indicate that something in the water quality has changed and warrants further re-testing (again, at a lab).