4.4.15 (HL)—Water Quality Index (WQI)

Vernier’s Water Quality Index converts nine parameter results to quality values, multiplies each by a weighting factor and sums them into one water-quality score.

Its nine parameters are temperature, pH, turbidity, total solids, dissolved oxygen, BOD, phosphates, nitrates and faecal coliforms. Inspect the component values as well as the weighted total, because a composite score can hide one dangerous result and other WQIs may use different parameters or scales.

A high overall score can coexist with unsafe faecal coliforms if that component is lightly weighted.

Only compare scores produced with the same index method, parameters, weights, scale and intended use.

A single composite score is not a substitute for component-level risk.